Scurvy and Cress

Without the subject of today's post, it's just possible that my home country of New Zealand could have had quite a different history. Sometimes, one shouldn't overlook the importance of cress.

Pepperwort Lepidium heterophyllum, copyright Anne Burgess.

Lepidium is a genus of herbs and subshrubs belonging to the Brassicaceae, the same family as cabbages, radishes and cauliflowers. The genus is found worldwide, and more than 150 species have been recognised to date. The fruit is a type of dry capsule called a silicle which is usually dehiscent (one subgroup of Lepidium, previously separated as the genus Cardaria, has indehiscent fruit), with strongly keeled or winged valves, and contains a single pendulous seed in each locule. The seeds are usually copiously covered in mucilage (Mummenhoff et al. 2001). Like other members of the Brassicaceae, Lepidium has not been overlooked for culinary uses. Leaves and stems of number of species in the genus, such as garden cress Lepidium sativum and dittander Lepidium latifolium, are used as pot or salad herbs. A South American species, maca Lepidium meyenii, is grown as a root vegetable.

Because of its wide distribution, some early authors suggested that Lepidium was a very ancient genus whose members had diverged with the break-up of the Mesozoic supercontinents. However, more recent phylogenetic analyses (Mummenhoff et al. 2001) have suggested just the opposite: the crown group of Lepidium may have originated in the Mediterranean-Central Asian region little more than two million years ago. The mucilaginous seeds of many species become sticky when damp, and can easily be carried long distances adhered to birds' feet and other such dispersal agents. Perhaps the most dramatic suggestion of intercontinental dispersal in the genus involves a clade of species found in Australia and New Zealand that phylogenetic analysis suggests originated via hybridisation between two divergent species—with one parent being native to South Africa and the other to California (Mummenhoff et al. 2004).

Cook's scurvy grass Lepidium oleraceum, copyright Andrea Brandon.

It was one of the members of the latter clade that played a small but significant role in New Zealand history. Lepidium oleraceum is an endemic New Zealand species that was once found growing over much of the country. It is commonly known as 'Cook's scurvy grass', because Captain James Cook was able to collect it while surveying New Zealand to provide vitamin C to stave off the scurvy that could have otherwise devastated his crew. Sadly, this once common plant is now extremely rare: the disappearance of mainland-nesting seabirds means that they are no longer around to provide the guano-enriched soils on which this plant thrived. It also proved extremely palatable to introduced herbivores. As a result, Cook's scurvy grass is now almost exclusively found on small offshore islets.

REFERENCES

Mummenhoff, K., H. Brüggemann & J. L. Bowman. 2001. Chloroplast DNA phylogeny and biogeography of Lepidium (Brassicaceae). American Journal of Botany 88 (11): 2051–2063.

Mummenhoff, K., P. Linder, N. Friesen, J. L. Bowman, J.-Y. Lee & A. Franzke. 2004. Molecular evidence for bicontinental hybridogenous genomic constitution in Lepidium sensu stricto (Brassicaceae) species from Australia and New Zealand. American Journal of Botany 91 (2): 254–261.

The Mancos Saltbush: Life in the Badlands

Thanks to your support, I am nearly 40% of the way towards success at my crowdfunding drive. But with only two days left on the clock, I'm going to need everyone's help if I'm to be succesful. Please visit my page at Experiment.com and consider offering your support!

Mancos saltbush Proatriplex pleiantha, from here.

Proatriplex pleiantha, the Mancos saltbush, is arguably not much to look at. It never grows very large (only about half a foot in height) and though a single plant may produce a lot of flowers, they are not very showy. Nevertheless, this little fleshy-leaved annual is something of a survivor. It grows on badlands in only a few localities in northern New Mexico and southern Colorado, and may be the only vegetation to be found on the eroded clays that it calls home. It persists in this hostile environment by not persisting; instead, each individual plant will produce hundreds, if not thousands, of seeds during its short life that may lie dormant in the soil for several years, waiting for the flash of rain that will allow it to emerge.

The Mancos saltbush was first described in 1950; its vernacular name refers to the original collection locality near the Mancos River. It was originally described in the genus Atriplex, a diverse cosmopolitan assemblage of herbs and shrubs in the family Chenopodiaceae commonly known as saltbushes and oraches (the garden orache or mountain spinach A. hortensis has long been grown as a vegetable in Europe). However, right from the start it was considered distinctive enough to be placed in its own subgenus, later raised to the status of a distinct genus by Stutz et al. (1990). A molecular phylogenetic analysis by Kadereit et al. (2010) later confirmed that Proatriplex pleiantha is not a direct relative of Atriplex, instead being associated with other small North American Chenopodiaceae genera Grayia and Stutzia. Features distinguishing Proatriplex from true Atriplex include the succulent leaves, the flowers being borne in groups of three to seven in the axil of a single bract, and the presence of a five-segmented perianth around female flowers (Atriplex flowers are borne singly to a bract, and lack a perianth).

Because of its restricted range, the Mancos saltbush may be vulnerable to disturbances in its habitat; for instance, one of its main population centres in New Mexico is in close proximity to the Navajo coal mine. Nevertheless, this species is not currently listed by the US Fish & Wildlife service as being of concern, due to its being locally abundant in the areas where it does occur. Surveys of this species have been complicated by the dependence of its germination on suitable weather conditions: in years with little rainfall, it may appear to be almost absent, but the advent of a wetter year may prove otherwise. All it takes is a decent drop of rain, and you may see the badlands bloom.

REFERENCES

Kadereit, G., E. V. Mavrodiev, E. H. Zacharias & A. P. Sukhorukov. 2010. Molecular phylogeny of Atripliceae (Chenopodioideae, Chenopodiaceae): implications for systematics, biogeography, flower and fruit evolution, and the origin of C₄ photosynthesis. American Journal of Botany 97 (10): 1664–1687.

Stutz, H. C., G.-L. Chu & S. C. Sanderson. 1990. Evolutionary studies of Atriplex: phylogenetic relationships of Atriplex pleiantha. American Journal of Botany 77 (3): 364–369.

Checker Mallows

The crowdfunding campaign for my research on New Zealand harvestmen is still active. So far we're about 25% of the way towards the goal! Please click on the link above, and do your part to support your favourite arachnologist.

Flowering spike of Sidalcea nelsoniana, copyright Rhiannon Thomas.

Regular readers may have noticed that it's been a bit quiet around here lately. The last few weeks at chez Christopher have been... hectic. I have been writing posts but not had the time to publish them. So over the next few days, you'll be seeing a bit of a run of short posts in quick succession. Keep your eyes out.

The handsome plant you see above is a representative of Sidalcea, a genus of about thirty species found in the north of Mexico and the western United States. Members of this genus are commonly known as checker mallows (apparently because of the pattern of veins on the petals of some species); in the British gardening trade, they are also known as prairie mallows. As indicated by their vernacular names, Sidalcea species belong to the mallow family Malvaceae, and are hence related to other flowering plants such as cotton or hibiscus. These affinities are also reflected by their genus name, which is a portmanteau of the names of two other genera of Malvaceae, Sida and Althaea. Checker mallows differ from other members of the Malvaceae in having flowers with stamens that separate from the stamineal column in two tiers, an inner and an outer ring.

Most species of checker mallow are herbs; a few may develop into subshrubs. The genus includes both perennial and annual species. Stems of checker mallows are mostly more or less erect though they are often basally reclining or decumbent towards the base;it is not uncommon for decumbent stems to become secondarily rooted into the ground and develop into spreading stolons (or 'rhizomes'). Flowers of checker mallows are usually various shades of purple; a small number of species have white flowers (or white forms may occur in usually purple species). Many species of this genus are supposed to be difficult to identify: hybridisation is not uncommon, and some species are quite plastic in their own right. Young plants may also have a quite different appearance, including differently shaped leaves, from mature plants.

Sidalcea campestris, photographed by Amy Bartow.

The primary monograph of Sidalcea was published by E. M. F. Roush in 1931. She divided the genus between three subgenera, two of which contained only a single species each with all the remainder placed in her subgenus Eusidalcea (since the publication of Roush's monograph, a third non-Eusidalcea species has been recognised). These species are all perennials that, among other features, lack the variation in leaf shape with growth seen in Eusidalcea. More recent molecular analyses have supported Roush's arrangement arangement (Andreasen & Baldwin 2003). However, they have not supported Roush's division of Eusidalcea into separate sections for the annual and perennial species; instead, it appears that one or the other habit (it is unclear which) has arisen multiple times.

Like other diverse plant genera found in the California region, Sidalcea has attracted a certain degree of research into its evolutionary dynamics. Comparison of evolutionary rates between species has found that, as might be expected, annual lineages evolve faster than perennial ones (Andreasen & Baldwin 2001). Most species within each life-history class appeared to evolve at similar rates to each other, except for three perennial species: the three non-Eusidalcea species referred to above. One of these species, Sidalcea stipularis (the only one not known to Roush in 1931) showed evidence of an unusually high evolutionary rate for a perennial; this species is restricted to a very small population (only a few hundred plants may exist in the wild) and may have been subject to a higher rate of effective genetic drift. In contrast, the other two species have diverged more slowly than expected. One of these species, S. malachroides, is a presumably slow-lived subshrub; the other, S. hickmanii, commonly germinates after fires from seeds that may have remained in the ground for a number of years. In both cases, the overall result is that particular genotypes may persist in the population longer than in species with a more rapid turnover.

Oregon checkerbloom Sidalcea oregana ssp. spicata, copyright Dcrjsr.

Another feature of Sidalcea population dynamics to have attracted interest is the occurrence in several species of gynodioecy, a phenomenon where some individuals of a population have flowers with both male and female organs whereas other individuals have female organs only. The persistence of such an arrangement raises questions: because hermaphroditic individuals have the potential to contribute to more reproductive pairings than female-only individuals, shouldn't the former end up out-competing the latter and eliminating them from the population? This has lead to the inference that some factor(s) must give the female-only individuals an advantage that allows them to persist. Ashman (1992) found in germination tests of Sidalcea oregana spp. spicata that seeds that came from female-only plants tended to germinate into healthier, more vigorous offspring than those from hermaphrodites. It may be that plants that can only produce seed by outcrossing are less vulnerable to the effects of inbreeding, or perhaps not having to invest energy in making pollen means that the parent can put more energy into producing seeds.

REFERENCES

Andreasen, K., & B. G. Baldwin. 2001. Unequal evolutionary rates between annual and perennial lineages of checker mallows (Sidalcea, Malvaceae): evidence from 18S–26S rDNA internal and external transcribed spacers. Mol. Biol. Evol. 936–944.

Andreasen, K., & B. G. Baldwin. 2003. Reexamination of relationships, habital evolution, and phylogeography of checker mallows (Sidalcea; Malvaceae) based on molecular phylogenetic data. American Journal of Botany 90 (3): 436–444.

Ashman, T.-L. 1992. The relative importance of inbreeding and maternal sex in determining progeny fitness in Sidalcea oregana ssp. spicata, a gynodioecious plant. Evolution 46 (6): 1862–1874.

Roush, E. M. F. 1931. A monograph of the genus Sidalcea. Annals of the Missouri Botanical Garden 18 (2): 117–244.

Mintbush Genus Limits

Victorian Christmas bush Prostanthera lasianthos, copyright Melburnian.

Despite (or perhaps because of) the severity of Australia's climate over much of the continent, the country has become famed for its wildflower displays. At the right time of year, the otherwise bleak landscape becomes a riot of form and colour. The display shown above belongs to a species of the genus Prostanthera, an assemblage of about 100 species of bushy shrubs (very rarely small trees) known as mintbushes, endemic to yet ubiquitous around Australia (new species continue to be described at fairly regular intervals). As suggested by their vernacular name, mintbushes belong to the mint family Lamiaceae, the same family as many well-known garden herbs such as sage, rosemary or thyme. Like these relatives, mintbushes have strongly aromatic foliage, due to the presence of glands secreting volatile oils on the leaves. However, the edibility of most species is unknown; I did find a couple of references to culinary uses of the round-leaved mintbush Prostanthera rotundifolia though it is not common (and a couple of comments in this thread suggest that it may be a bit pungent for regular use). Certainly, to push the pun in this post's title far further than it deserves, there is no evidence of mintbush gin.

Prostanthera species are most readily recognised by their flowers (Wilson et al. 2012). The calyx at the base of the flower has the sepals fused so that it is shaped as two lips, an upper and a lower. The corolla of petals has five lobes, two in the upper lip and three in the lower. There are four anthers, which often (though not always) have a distinct basal appendage; it is this appendage that gives the genus its name (from the same Greek word that gives us the term 'prosthetic'). Different species have flowers in a wide range of colours, and many Prostanthera species have become popular ornamentals.

Flower of scarlet mintbush Prostanthera aspalathoides, copyright Patrick Kavanagh.

Prostanthera is a member of a tribe of Australian Lamiaceae known as the Westringieae, members of which have a dry fruit splitting into four sections (Conn 1984). The two-lobed calyx of Prostanthera separates it from most other genera that have been recognised in the Westringieae except for a small genus called Wrixonia. The only significant difference between Wrixonia and Prostanthera is that whereas the latter retains four fertile anthers, the former has one pair of anthers sterile and reduced. A molecular phylogenetic analysis by Wilson et al. (2012) found that Wrixonia species were nested within Prostanthera, raising doubt about whether Wrixonia should be recognised as a separate genus. Also of interest was the relationship between the two sections into which Prostanthera has been divided: section Prostanthera and section Klanderia. These sections differ in characteristics of their flowers. Prostanthera section Prostanthera has flowers that are white, mauve or blue, with a corolla in which the central lower lobe is longer than the others so the overall appearance is similar to an orchid (such as in the P. lasianthos at the top of this post). In section Klanderia, the flowers are green, yellow or red, and the two upper lobes of the corolla are the longest so the appearance of the flower is more tubular (such as in the P. aspalathoides just above). Some authors have regarded the difference between two sections as enough to warrant recognised section Klanderia as a separate genus (in which case it becomes known as Cryphia, because botanical nomenclature is complicated like that). The two sections differ in flower morphology because they differ in pollinator type: flowers of section Prostanthera are pollinated by insects, whereas flowers of section Klanderia are pollinated by birds. Again, Wilson et al. (2012) found that the larger section Prostanthera, which retains the ancestral pollinator type, is paraphyletic with regard to the derived section Klanderia.

REFERENCES

Conn, B. J. 1984. A taxonomic revision of Prostanthera Labill. section Klanderia (F.v.Muell) Benth. (Labiatae). J. Adelaide Bot. Gard. 6 (3): 207–348.

Wilson, T. C., B. J. Conn & M. J. Henwood. 2012. Molecular phylogeny and systematics of Prostanthera (Lamiaceae). Australian Systematic Botany 25: 341–352.

Why is an Oak like a Cassowary?

Beach casuarina Casuarina equisetifolia bearing flowers and cones, copyright Atamari.

When one thinks of the Australian vegetation, one might think of towering eucalypts or hardy acacias. One might contemplate unwelcoming spinifex or vibrant grevilleas. But perhaps few groups of plants are so distinctively Australian as the Casuarinaceae, the casuarinas or she-oaks. Members of this family are also found in south-east Asia and the Pacific Islands, but it is in Australia that they reach their highest diversity.

Casuarinas are also unmistakable. They are flowering plants, but they are wind-pollinated and the flowers are highly reduced, being borne in small clusters or spikes. The clusters of fruits, when mature, look more like a miniature pine cone than anything else. The trees that bear these cones also look a bit like pines themselves, with their narrow photosynthetic branches (cladodes) bearing a superficial resemblance to pine needles. The leaves proper are reduced to tiny teeth arranged around nodes or joints on the branches. The outer layer of the cladodes is composed of a thick cortex which together with the needle-like morphology helps resist desiccation. The name of the family refers to the resemblance of their branches to the hair-like feathers of a cassowary Casuarius. Casuarinas are so distinct from other flowering plants that their affinities were long uncertain, though more recent studies have suggested a relationship to other wind-pollinated trees in families such as the Betulaceae (Steane et al. 2003).

In line with their drought-resistant mien, casuarinas are most often found growing in arid and/or coastal regions. The most widespread species, the beach she-oak Casuarina equisetifolia, is found along coastlines from the Bay of Bengal to Polynesia. Their persistance in harsh conditions is also assisted by the presence of nodules on their roots containing bacteria of the genus Frankia, that function like the Rhizobium in root nodules on legumes to fix nitrogen from the atmosphere. Casuarinas also resemble pine trees in forming a mat around their base of fallen cladodes that restricts the growth of competing vegetation.

Desert oaks Allocasuarina decaisneana, copyright Cgoodwin.

Until relatively recently, casuarinas were all classed in a single genus but most authors now recognise four genera in the family. The most distinctive, whose position as sister to the remaining genera is confirmed by molecular analyses (Steane et al. 2003), is Gymnostoma, which contains eighteen species found from south-east Asia to Queensland and Fiji. Whereas other genera of Casuarinaceae have the stomata on the cladodes hidden within deep longitudinal grooves, Gymnostoma has much shallower grooves on the cladodes and the stomata more or less exposed. As such, it is less resistant to desiccation than the other genera. Gymnostoma has four of these grooves on each cladode, corresponding to four leaf-teeth around each node, so the cladodes also tend to have a squarish cross-section.

The second-most divergent genus, Ceuthostoma, contains just two species found from Palawan and Borneo to New Guinea. Ceuthostoma resembles Gymnostoma in having four teeth around each node, but resembles the remaining two genera, Casuarina and Allocasuarina, in having the stomata hidden within deep grooves. In Casuarina and Allocasuarina, the number of teeth around each node is generally increased (up to twenty in Casuarina), meaning that the cladodes are more rounded than square. As noted by Steane et al. (2003), rounder cladodes with more grooves mean that the opening of each groove is narrower, further improving desiccation resistance. Casuarina and Allocasuarina are most readily distinguished by the appearance of their seeds, which are paler and dull in Casuarina but dark brown or black and shiny in Allocasuarina. Allocasuarina is the most diverse genus of the family, with over fifty species endemic to Australia. Casuarina contains fewer species but is more widespread. Steane et al.'s molecular analysis suggested a division within Casuarina between two main clades, one of which was restricted to Australia while the other was primarily composed of Indomalesian species (as well as C. equisetifolia which, as noted above, is found damn near everywhere).

Borneo ru Gymnostoma nobile, from natureloveyou.sg.

Fossils of Casuarinaceae date back to the Palaeocene epoch, and indicate that the family was more widespread in the past with species known from the Eocene of South America and the Miocene of New Zealand. Casuarinaceae-like pollen is also known from the Palaeogene of southern Africa and Antarctica. The South American species have been assigned to the living genus Gymnostoma; the New Zealand species, though originally assigned to Casuarina, is probably also more closely related to Gymnostoma (Zamaloa et al. 2006). Though dominant in the modern flora, the drought-resistant clade of the other three genera is probably of more recent origin, and has probably only ever been unique to the Australasian region.

And I've just realised that I haven't answered the question in the title to this post. As I noted above, an alternate vernacular name for these trees to 'casuarina' is 'she-oak'. I used to wonder why this should be, seeing as casuarinas look about as unlike oaks as you might care to imagine. A good summary of the solution can be found in this newspaper column from the Western Mail of 1914. Though some have suggested that 'she-oak' may be a corruption of an Aboriginal word (despite no such word having been put on record), the more simple explanation is that even if the tree itself doesn't look like an oak, the wood that comes out of it does.

REFERENCES

Steane, D. A., K. L. Wilson & R. S. Hill. 2003. Using matK sequence data to unravel the phylogeny of Casuarinaceae. Molecular Phylogenetics and Evolution 28: 47–59.

Zamaloa, M. del C., M. A. Gandolfo, C. C. González, E. J. Romero, N. R. Cúneo & Peter Wilf. 2006. Casuarinaceae from the Eocene of Patagonia, Argentina. International Journal of Plant Sciences 167 (6): 1279–1289.

Stars and Blessings

Yellow starthistle Centaurea solstitialis, copyright Franco Folini.

The first thing that struck me when I was looking up material on Centaurea was how evocative some of the vernacular names associated with this genus are: starthistle, blessed thistle, dusty miller, sweet sultan. Centaurea, the starthistles and knapweeds, is a genus of composite-flowered plants native to Eurasia and northern Africa, with the highest diversity of species in the Mediterranean region. A handful of species have been spread to other parts of the world in association with humans; a handful of these are significant pasture pests such as spotted knapweed C. maculosa and yellow starthistle C. solstitialis, whereas others such as dusty miller C. cineraria are grown as garden plants. Centaurea is a large genus: depending on how you count them, it may contain anywhere between 300 and 700 species. The greater number of species are perennial herbs, but the genus varies from small spiny shrubs to low spreading annuals (Wagenitz 1986). Some arise from a single central tap-root; others grow from spreading rhizomes. Some species have spiny leaves and conform to our general idea of a 'thistle'; others do not. The leaves are often deeply divided at the base of the plant, becoming entire towards the top. Flowerheads may be borne singly or in a corymbiform arrangement (a flat-topped cluster); the phyllaries (the bracts surrounding the flowerhead) often extend outwards around the head, and may be themselves tipped with spines.

Squarrose knapweed Centaurea triumfettii, copyright Kristian Peters.

With a genus of this size, it should be hardly surprising that taxonomic complications are involved. Long recognised as morphologically diverse, it has been confirmed as polyphyletic by more recent molecular analyses (Garcia-Jacas et al. 2001). The majority of Centaurea species fall within a single derived clade within the composite subtribe Centaureinae, united both by molecular data and by a number of morphological synapomorphies including adaptations for myrmecochory, dispersal of the seeds by ants (the seeds carry an attached oily body called an elaiosome; ants carry the seeds back to their nest where they may eat the elaiosome but leave the seed to sprout). A handful of species, though, lack these synapomorphies and lie in scattered segregate clades among the remainder of the Centaureinae. Some of these segregate clades, such as the former section Psephellus, have been straightforwardly promoted to the status of separate genera. One small segregate clade, however, is a little more problematic because it happens to include the north African Centaurea centaurium, the original type species of the genus Centaurea. Under normal circumstances, then (other than lumping the entirety of centaureines in a single genus), the name Centaurea would apply only to this small clade (including only about a dozen species) while the hundreds of species in the main 'Centaurea' clade would have to be renamed. In this case, the name with priority for this large clade would be Cnicus, generally used to date for only a single species, the blessed thistle Cnicus benedictus (no, I haven't been able to establish why it is called the 'blessed thistle'; I have found references to a tradition of medicinal use for this species, including its supposedly encouraging milk production in nursing mothers, but I haven't been able to confirm if this is the reason for the name). In order to stave off this nomenclatural turmoil, it has been proposed that the official type species of Centaurea be changed to a member of the main clade (Greuter et al. 2001), so this clade keeps the name Centaurea (and the blessed thistle becomes referred to as Centaurea benedicta) whereas the small clade including the prior type species becomes known as the genus Rhaponticoides. I haven't found whether a final decision has been made on this proposal (the process for such nomenclatural decisions is a bit more involved for plants than animals, requiring an open vote at an international botanical conference rather than just being decided on directly by a select committee) but it seems to have general support. Less certain is the status of the cornflowers of the section Cyanus, which some have proposed recognising as a separate genus but which is closely related to the main clade, making the case for its separation a bit less compelling.

REFERENCES

Garcia-Jacas, N., A. Susanna, T. Garnatje & R. Vilatersana. 2001. Generic delimitation and phylogeny of the subtribe Centaureinae (Asteraceae): a combined nuclear and chloroplast DNA analysis. Annals of Botany 87: 503–515.

Greuter, W., G. Wagenitz, M. Agababian & F. H. Hellwig. 2001. (1509) Proposal to conserve the name Centaurea (Compositae) with a conserved type. Taxon 50: 1201–1205.

Wagenitz, G. 1986. Centaurea in south-west Asia: patterns of distribution and diversity. Proceedings of the Royal Society of Edinburgh, Section B, Biological Sciences 89: 11–21.

I Said Primrose-Willows, Darling

The plant shown in the photo above (copyright Forest and Kim Starr) is Ludwigia octovalvis, commonly known (along with other species in the same genus) as primrose-willow. This is a very common plant in tropical and subtropical regions around the world; indeed, it is so widespread that we have little idea where in the world it originated*. The name 'primrose-willow' derives, of course, from its combination of primrose-like flowers with willow-like leaves, but it is no close relation to either. Primrose-willows belong to the Onagraceae, the same plant family as evening primrose or fuchsias. Ludwigia octovalvis is a shrubby plant, sometimes growing up to four metres in height. Lower parts of the stem may become woody with age, but the greater part of the plant is herbaceous. It prefers to grow in damp habitats, in swampy soil or alongside streams, even rooted in ponds. The seeds are minute and easily spread by water or mixed in with other materials. They are also durable: Raven (1977) refers to the possibility of propagating Ludwigia from seeds preserved in herbarium specimens.

*Which, if one were of a panbiogeographical bent, might be taken to indicate that it has survived unchanged since the Triassic at least.

Ludwigia octovalvis may even grow as floating mats upon the surface of water. The floating roots then produce spongy, upright branches called aerophores. These have been interpreted as floatation devices, but the plant is apparently perfectly buoyant without them. It is more likely that they allow oxygen to reach the waterlogged roots. The lower part of the stem may also become covered in aerenchyma, porous tissue that also aids in the diffusion of gases. If conditions dry up and the plant becomes rooted in the ground, the aerophores disappear and the roots resume their normal rootly business.

Close-up of flower of Ludwigia octovalvis, copyright Bob Peterson.

Primrose-willows are generally toxic to humans. In the usual way, I have come across references to Ludwigia octovalvis being used folk-medicinally, mostly to help with ailments of the digestive tract such as diarrhoea and worms. A quick look through Google Scholar indicates that this has lead to a certain degree of pharmaceutical research, but so far this doesn't seem to have lead to much major commercial application. At the present point in time, the main economic impact of Ludwigia octovalvis is as a weed. It can grow mixed in with fields of crops such as rice and taro, or particularly lush patches of primrose-willow may clog up waterways. On the flipside, I did find this summary of the species that notes that, "Its yellow flowers add a splash of color to areas often devoid of colorfully flowering plants".

REFERENCES

Raven, P. H. 1977. Onagraceae. Flora Malesiana, ser. I, 8 (2): 98–113.

Melastomes and Pals

Princess flower Tibouchina heteromalla, copyright João Medeiros.

For most botanists currently working on flowering plants, the default taxonomic framework for their studies is the classification published by the Angiosperm Phylogeny Group. This is not the only classification for angiosperms proposed in recent years, but it is the most widely recognised, and it is the one that all its competitors are compared to. If there is one major deficiency of the Angiosperm Phylogeny Group classification, it is that it eschews the use of formal categories between 'orders' (which it tends to define broadly) and 'families'. As such, there are a number of well-supported clades that require one to turn to alternative classifications for suitable names.

Crypteronia paniculata, copyright Tony Rodd.

The Melastomatineae, as recognised by Reveal (2012), for instance, is a clade of mostly tropical and subtropical plants within the Myrtales commonly recovered by molecular phylogenetic analyses. Most of its members are included in the pantropical family Melastomataceae, but it also includes three much smaller and more localised families: the southeast Asian Crypteroniaceae, the western Neotropical Alzatea and the African Penaeaceae. Some authors also divide the Melastomataceae into two families Melastomataceae and Memecylaceae, but as the two groups are universally accepted as sister clades this is purely a matter of taste. Morphological characters uniting the families are few (see the Angiosperm Phylogeny Website). Many accumulate aluminium in the leaves, to the extent that the leaves of the small tree Memecylon edule were used in India as a mordant for fixing dyes to cloth. The flowers lack nectaries, and when nectar is produced in the Melastomataceae it exudes from locations such as the anthers or the corolla. Some Olisbeoideae (the Memecylaceae of other classifications) produce oil from glands on the anthers that is collected by pollinators in lieu of nectar. In the South American genus Axinaea, the anthers have a sugary appendage that is eaten by tanagers; as they attack it, a puff of pollen dusts their head. The anthers of Melastomataceae are often distinctly coloured from the rest of the flower, and arranged in a distinctive seried row on one side of the flower. The Melastomatoideae (i.e. Melastomataceae sensu stricto) also have distinctive leaves, with three or more strong longitudinal veins arising from the leaf base and connected by cross-veins.

Mountain hard pear Olinia emarginata, copyright H. Robertson. Olinia leaves smell of almonds when crushed, due to the presence of a cyanogenic compound.

Though Melastomataceae are often significant members of the tropical forest understorey, they tend not to have much direct economic significance for humans. Some, such as the princess flowers or glory trees of the genus Tibouchina, are grown as ornamentals. The hard pear Olinia ventosa of the Penaeaceae (no, I don't know why it's called that) is grown as a shade tree in South Africa. A few species of Melastomataceae are significant invasive weeds in warmer regions, including such luminaries as the Straits rhododendron Melastoma malabathricum and the evocatively-named Koster's curse Clidemia hirta. The velvet tree Miconia calvescens has earned itself the label of the 'purple plague' in Hawaii, where it over-runs native forest.

REFERENCE

Reveal, J. L. 2012. An outline of a classification scheme for extant flowering plants. Phytoneuron 37: 1–221.

Teasels and Scabious: the Dipsacaceae

Scabiosa cretica, copyright Ori Fragman Sapir.

As recognised plant families go, the Dipsacaceae is not a particularly large one. It includes only a few hundred species, of which the majority are found in arid regions around the Mediterranean and the remainder elsewhere in Africa and Eurasia. The economic significance of the family is also relatively low. Some species are cultivated as ornamental plants. Dipsacus fullonum, teasel, gets its vernacular name because its bottle-brush-like flower-heads were used to tease the fibres of woollen cloth. Various species of Dipsacaceae, particularly the genus Scabiosa, are known as 'scabious' because they were apparently once used somehow in treating scabies. I also came across a reference in Duke (2008) to Syrian scabious Cephalaria syriaca having had a certain notoriety in the past due to its seeds being similar in appearance to wheat grain, meaning that they could be inadvertently sown into fields, or impart an unpleasant taste if ground into flour.

Flowers and fruits of Sixalix atropurpurea, copyright Manuel M. Ramos. Members of this genus grow on sand; their fruits have a reduced membranous wing, and disperse by rolling.

Nevertheless, the Dipsacaceae are not without their points of interest. One intriguing characteristic of the family is that they bear numerous small flowers clustered onto a single shared receptacle, similar to those of the much more diverse Asteraceae. Like Asteraceae, there may even be a differentiation in the appearance of flowers on the inner part of the receptacle from those around the outer rim. The Dipsacaceae are not directly related to the Asteraceae; rather, the two families have developed their capitate flower-heads independently. Which is not to say that they are incomparable: species of both Asteraceae and Dipsacaceae exhibit duplications of genes that are believed to affect the development of floral symmetry (Carlson et al. 2011), and it is possible that similar processes have lead to the evolution of compound flower-heads in both.

Flowers and fruits of Scabiosa sicula, copyright Jose Rodriguez. The fruiting head in focus shows the membranous wings that function in dispersal.

Past authors have divided the Dipsacaceae into three tribes, largely on the basis of characters related to seed dispersal. Each of the small flowers on a dipsacacean flower-head develops into a dry fruit containing a single seed. The epicalyx (an outer protective layer of the flower base) persists as an outer coating of the mature fruit, like a second skin. In the largest of the three previously recognised tribes, the Scabioseae, the epicalyx is often modified for wind dispersal, either by plumose hairs on top of a dorsal tube (the same sort of set-up as seen in dandelions) or by a membranous wing around the fruit. In contrast, the fruit of the genus Knautia, widow flowers, which has been placed in its own separate tribe, bears an elaiosome, a fleshy, hemispherical lump. The elaiosome attracts ants, who carry the fruit away to their nest; after the ants have eaten the elaiosome, the remaining seed is able to germinate where they leave it. Finally, the third tribe Dipsacaceae includes only the genera Dipsacus and Cephalaria; the mature fruit of these genera lack adaptations for either wind or ant dispersal, and seed dispersal is largely controlled by the break-up of the flower-head itself.

Bassecoia bretschneideri, copyright Dave Boufford.

More recent molecular analyses, however, have not entirely supported this three-way division of the Dipsacaceae (Carlson et al. 2009). While Knautia and the Dipsaceae are both likely to be monophyletic, the Scabioseae are not. Instead, a small clade including the eastern Asian genus Bassecoia is sister to the remaining members of the family. These fall into two major clades: one, that has been referred to as the Scabioseae 'sensu stricto', includes the majority of the taxa previously included in the Scabioseae, such as Scabiosa, Lomelosia and Pterocephalus. The other clade, which has been dubbed the 'dipknautids', includes Knautia and the Dipsaceae, together with a few smaller 'ex-Scabioseae' genera. While the original Dipsacaceae may have been wind-dispersed, they have not been above looking at alternatives.

REFERENCES

Carlson, S. E., D. G. Howarth & M. J. Donoghue. 2011. Diversification of CYCLOIDEA-like genes in Dipsacaceae (Dipsacales): implications for the evolution of capitulum inflorescences. BMC Evolutionary Biology 11: 325. doi:10.1186/1471-2148-11-325.

Carlson, S. E., V. Mayer & M. J. Donoghue. 2009. Phylogenetic relationships, taxonomy, and morphological evolution in Dipsacaceae (Dipsacales) inferred by DNA sequence data. Taxon 58 (4): 1075-1091.

Duke, J. A. 2008. Duke's Handbook of the Medicinal Herbs of the Bible. CRC Press.

What is Inula verbascifolia?

By recommendation of the Committee for Spermatophyta (Brummitt 2005), this is. Photograph by L.R.

Inula verbascifolia is a herbaceous, composite-flowered plant from the eastern Mediterranean. It is mostly found in the Balkan region, but it also reaches into south-eastern Italy and Anatolia. It is closely related to another Greek species, I. candida, and the two have been treated as a single species, but they can be distinguished by features of the leaves (Tan et al. 2003).

The reason for my question, though, is that Inula verbascifolia has been the subject of an application to have its name conserved (Tan et al. 2003). The rules for naming organisms are often assumed to be complicated, and to a certain extent they are, but the underlying principles can be summed up into two rules: (1) every species should have one name that is different from all other species, and (2) when two names are in conflict, the older name is the correct one. However, like all rules of life, sometimes the best thing to do is not follow the rules. Maybe using the older name would be too confusing, if the newer name is much the better known. To account for such scenarios, all of the various bodies governing the naming of organisms (there are separate bodies for animals, plants and bacteria) make allowances for researchers on the organisms concerned to apply for the rules to be temporarily set aside in some way.

In the case of Inula verbascifolia, the plant currently known by that name was not the first to be called that. The German botanist Heinrich Haussknecht recognised the Balkan species as Inula verbascifolia in 1895. Prior to that, it gone under the name of Conyza verbascifolia, coined by Carl von Willdenow in 1803. However, in 1813 Jean Poiret of France had used the name I. verbascifolia for a plant growing the gardens of the Jardin des Plantes in Paris that had originally come from the Caucasus. 1813 beats 1895, so under strict application of the rules the name Inula verbascifolia should apply to the Caucasian plant, not the Balkan one. But the Caucasian plant had not been known by this name since 1819, whereas the Balkan plant was well-known by that moniker, so Tan et al. (2003) applied for the Balkan plant to be allowed to keep it.

I should point out that I'm an animal taxonomist by training, so I have only a basic awareness of the rules that apply to naming plants. One thing that interests me in this case is that things would have played out differently had the organisms in question been animals. The Zoological Code differs from the Botanical Code in that it doesn't regard the genus name as an integral part of the species name, so even if a species name is moved between genera, it still takes its priority from when it was first coined. In this case, for the Zoological Code the important date would not be 1895 when Haussknecht transferred verbascifolia to Inula, but 1803 when Willdenow called it verbascifolia in the first place. So under the Zoological Code, Willdenow's verbascifolia would be older than Poiret's verbascifolia, and there would be no need for the former to be specially upheld.

Another difference between the Zoological and Botanical Codes is in the process of deciding on applications. In the Zoological Code, an appointed body of taxonomists (the Commission) directly makes each decision themselves. In the Botanical Code, on the other hand, each application goes to a Committee (there are separate committees for seed plants, algae, fungi, etc.) who then vote on a recommendation whether or not to accept the application. The final decision is not made by the Committee, but is voted on by the attendees of the next International Botanical Congress, a conference that anyone is allowed to attend (if they're willing to pay the attendance fee, of course). In the case of Inula verbascifolia, the Committee on Spermatophyta recommended that the application be accepted (Brummitt 2005), but I don't know if it has been finally voted upon. I also don't know if Congress votes often go against Committee recommendations (I wouldn't expect them to, but passions can run high in the world of taxonomy).

Inula verbascifolia ssp. methanea, photographed by Giorgos Gioutlakis. (Update: Christine K. tells me that this photo has been misidentified. See her comment below.)

Tan et al.'s application had to save more than just the species name. Haussknecht's Inula verbascifolia shows enough variation over its range that it has been divided between five subspecies. The photograph at the top of this post, taken in Italy, shows the type subspecies I. verbascifolia ssp. verbascifolia. The photograph just above shows another subspecies from Greece. But when Tan et al. looked at the original specimens examined by Willdenow, they found that they did not belong to the subspecies that had since come to be known as the type. Therefore, they designated a new type specimen belonging to the recognised type subspecies: otherwise ssp. methanea might have had to be called ssp. verbascifolia, and ssp. verbascifolia would have had to be called something else. It is possible that Willdenow had himself seen a specimen of the type subspecies that has since been lost: according to Tan et al., he gave the distribution of Conyza verbascifolia as Sicily, Greece and Armenia. Tan et al. pointed out that Inula verbascifolia's distribution in Italy is in Gargano, not Sicily, so regarded Willdenow's record as an error. What they had evidently overlooked was that, in 1803, Gargano was still part of the Kingdom of Sicily.

And if you're still around after all of that, then you may find the newest cartoon from xkcd oddly apropos:

REFERENCES

Brummitt, R. K. 2005. Report of the Committee for Spermatophyta: 56. Taxon 54 (2): 527-536.

Tan, K., J. Suda & T. Raus. 2003. (1582) Proposal to conserve the name Inula verbascifolia (Willd.) Hausskn. against I. verbascifolia Poir. (Asteraceae) and with a conserved type. Taxon 52: 358-359.

Malpighiales: A Glorious Mess of Flowering Plants

Ixonanthes reticulata, from here.

There is no denying that the advent of molecular analysis revolutionised the world of plant phylogeny. Previously an uncertain landscape of shifting sands, beset by the eroding forces of convergent evolution and morphological plasticity, the higher relationships of flowering plants have begun to resolve into a much clearer view than before. But some of the revealed vistas have been unexpected, and have led to quagmires of their own.

The Malpighiales are one clade that has become generally recognised as a result of molecular analyses, but remain almost impossible to characterise morphologically. Part of that difficulty is a consequence of sheer diversity: the clade includes about 16,000 species worldwide. The bulk of these species are tropical; it has been estimated that 40% of the world's tropical rain-forest understory is composed of Malpighiales (Xi et al. 2012). Only a relative minority of Malpighiales are found in more temperate parts of the world, though that minority still includes such familiar plants as violets, willows and spurges. The ranks of Malpighiales include some of the most bizarrely modified of all flowering plants: the endoparasitic Rafflesiaceae and the aquatic Podostemaceae.

Fruit of the jellyfish tree Medusagyne oppositifolia, photographed by Christopher Kaiser-Bunbury. The jellyfish tree is restricted to the Seychelles and critically endangered; the few surviving trees occupy marginal habitat where seedling germination seemingly cannot occur.

Though molecular analyses have been fairly consistent in supporting the Malpighiales as a whole, relationships within the Malpighiales long proved more recalcitrant. As a result, its species have been placed in up to 42 different families, these families varying wildly in diversity. At one end of the scale, the Euphorbiaceae has been home to over 5700 species, even in its modern restricted sense (earlier botanists recognised a Euphorbiaceae that was considerably larger). At the other end, the Malesian vine Lophopyxis maingayi and the jellyfish tree Medusagyne oppositifolia of the Seychelles have each been considered distinctive enough and of uncertain enough affinities to be placed in their own monotypic families. Many of these families could only be placed within the Malpighiales as part of a great polytomy, an unresolved mess of relationships at the base of the clade.

Herbarium specimen of Centroplacus glaucinus, from here. This species has a restricted range in West Africa; its closest relatives belong to the genus Bhesa in south-east Asia.

A major advance in our understanding of malpighialean phylogeny was made just recently by Xi et al. (2012), who were able to obtain a more resolved phylogenetic tree than previous studies through the use of data from a large number of genes (they also ignored the Rafflesiaceae; those guys just cause trouble). Their results suggested a division of the Malpighiales between three basal clades. The smallest of these includes relatives of the families Malpighiaceae and Chrysobalanaceae. Few members of this clade are familiar outside the tropics. Some are known for their edible fruit, such as the coco plum Chrysobalanus icaco, the nance Byrsonima crassifolia, the Barbados cherry Malpighia emarginata and the butter-nut Caryocar nuciferum. In contrast, the southern African gifblaar Dichapetalum cymosum contains toxic sodium monofluoroacetate and is regarded as a serious threat to livestock.

Small individual of the mangrove Kandelia candel, photographed by Dans.

The next clade includes families relatied to the Clusiaceae, Ochnaceae and Erythroxylaceae. The latter family is closely related to (and sometimes synonymised with) the Rhizophoraceae, a small but significant family that dominates among the tropical mangroves. The Erythroxylaceae is itself most notorious for including the coca plant Erythroxylum coca, the source of the drug cocaine*. The clusioid families include the Clusiaceae, Hypericaceae and Calophyllaceae, treated in older sources as a single family Guttiferae but currently treated as separate families owing to the paraphyly of such a grouping to the families Bonnetiaceae and Podostemaceae. The name 'Guttiferae' refers to the production of resin by many clusioids. In some species, these resins are produced in the flowers in lieu of nectar and are collected for nest-building by visiting bees. Economically significant clusioids include the mangosteen Garcinia mangostana and the St John's wort Hypericum perforatum, which has been grown commercially in some parts of the world for its supposed medicinal properties but is regarded in other parts of the world as a highly undesirable weed.

*Not raisins.

Flower of Rhizanthes infanticida, a smaller relative of Rafflesia, growing from host roots on the forest floor in Thailand, from here. Further buds are visible as reddish balls closer to the tree.

The third clade, and the largest by a considerable margin, includes such families as the Euphorbiaceae, Violaceae and Salicaceae. Noteworthy examples of this clade also include the passion fruit Passiflora edulis, and the flax plant Linum usitatissimum. The Euphorbiaceae, as alluded to above, were previously considered to include taxa more recently treated as the separate families Putranjivaceae, Phyllanthaceae, Picodendraceae and Peraceae. The Putranjivaceae were placed by Xi et al. (2012) in the Malpighiaceae-Chrysobalanaceae clade, and so are not close relatives of the Euphorbiaceae sensu stricto. The remaining families are closer, but modern authors would prefer to keep them separate as the demands of monophyly would then require the Euphorbiaceae be further enlarged to include the Linaceae and Rafflesiaceae. Nobody wants a Rafflesia in their family.

REFERENCE

Xi, Z., B. R. Ruhfel, H. Schaefer, A. M. Amorim, M. Sugumarane, K. J. Wurdack, P. K. Endress, M. L. Matthews, P. F. Stevens, S. Mathews & C. C. Davis. 2012. Phylogenomics and a posteriori data partitioning resolve the Cretaceous angiosperm radiation Malpighiales. Proceedings of the National Academy of Science of the USA 109 (43): 17519-17524.

The Wool Plants

Vegetable lamb, as illustrated in The Travels of Sir John Mandeville (ca 1360).

Medieval legend in Europe spoke of a strange animal that could supposedly be found far off in central Asia: the vegetable lamb. According to legend, this was an animal much like an ordinary sheep except that it grew directly from a plant, to which it remained attached by the umbilical cord. The vegetable lamb would sustain itself by grazing on nearby vegetation but when this was depleted, as the lamb could not move away from the plant to which it was attached, the lamb would die. How such a pointlessly self-defeating organism was supposed to persist does not appear to have concerned the medieval lexicographers; presumably it was supposed to be allegorical of something.

Opening fruit of Gossypium hirsutum, photographed by B. P. Schuiling.
Part of the reason for the legend's persistence, however, was that there was indeed a form of 'wool' that came from a plant: cotton. The cotton genus Gossypium comprises about fifty species found in tropical and subtropical regions around the world (Wendel et al. 2010). Members of the genus vary from herbaceous perennials to small trees. The genus is divided into four subgenera, most of which are geographically distinct. The subgenus Gossypium is found in Africa and Arabia, subgenus Sturtia in Australia, and subgenus Houzingenia in the Americas. These three subgenera between them include the diploid cotton species; the fourth subgenus Karpas is also found in the Americas but differs in containing tetraploid species. Genetic evidence indicates that the subgenus Karpas arose at some point in the very recent past (within the last one or two million years) from a single hybridisation event between a species of subgenus Gossypium and one of Houzingenia, probably as a result of some chance dispersal event from Africa. Gossypium seeds seem well suited to dispersal: seeds of the Hawaiian Island species G. tomentosum have apparently germinated after being kept immersed in artificial seawater for three years (Wendel et al. 2010)! This same predicection for dispersal has resulted in the tetraploid species rapidly becoming widespread despite their recent origin, and in producing two species in remote locales: the Hawaiian G. tomentosum is directly related to the mainland G. hirsutum, while the Galapagos G. darwinii is sister to the mainland G. barbadense.

Levant cotton Gossypium herbaceum, photographed by H. Zell.

Commercial cotton is grown from four species of Gossypium, which may have each been domesticated independently in prehistoric times. All Gossypium species produce seeds with a covering of fuzzy hairs, but seeds of the two Old World diploid species G. herbaceum and G. arboreum also possess an outer layer of longer, flatter hairs that can be woven into thread. It was one of these two species, or possibly some now-extinct close relative, that made the crossing over the Atlantic to become one ancestor of the tetraploid species; as a result, the tetraploid species also possess these long outer hairs. Two of the tetraploid species, G. barbadense and G. hirsutum, were also domesticated, and the latter of these is now by far the most abundant cotton species in cultivation*.

*In case you were wondering, no-one seems to have suggested that the island species related to the two American domesticates might have been human-dispersed.

Sturt's desert rose Gossypium sturtianum, from here.

Other diploid Gossypium species do not possess this longer outer hair layer, only the inner short layer, and are not sources of commercial cotton (though hybrids with some of these species have been used to breed desirable genetic traits into the commercial species). In one group of Australian species (the section Grandicalyx) found in the Kimberley region of northern Western Australia, the hair layer has become very sparse and the seeds are almost hairless. These seeds also possess fatty bodies called eliosomes that are attractive to ants, and the plants are dispersed by having hungry ants carry their seeds away. Grandicalyx species are seasonal herbs, dying off above ground during droughts only to resprout from their thick root-stock. Other Australian species include the Sturt's desert rose Gossypium sturtianum, the floral emblem of Australia's Northern Territory.

Gossypium gossypioides, from here.

As with other plant groups, hybridisation appears to have been a recurring factor in the evolution of Gossypium. The diploid Gossypium species have been divided between eight genome groups, hybrids between which are generally not viable (though not unknown: the parents of the tetraploid lineage, for instance, belonged to separate groups). However, genetic studies of some Gossypium species have identified discrepancies where a species may possess the nuclear genome of one group, but the chloroplast genome of another. For instance, the North American species G. gossypioides resembles other New World species in its nuclear genome, but has chloroplasts related to those of G. herbaceum or G. arboreum (which it may have acquired as a result of the same hybridisation event that produced the tetraploid species*). This phenomenon, which has been called cytoplasmic introgression, may have arisen in cotton through a process called semigamy. Semigamy is a particular form of apomixis (reproduction without fertilisation) in which sperm and egg cells fuse cytoplasmically, but their nuclei remain distinct (Curtiss et al. 2011). These nuclei will eventually be segregated by cell division, resulting in offspring that are mosaics of male- and female-line genomes. Over time, selection or drift may produce a homogenous population that retains the nuclear genome of one ancestor, but the cytoplasmic heritage of the other.

*The American parent of the tetraploids has more usually been identified as G. raimondii, a South American species, but G. raimondii is the direct sister species of G. gossypioides. It may be that G. gossypioides is the true parent of the tetraploids, or it may be that it too is derived from G. raimondii or its parent stock).

REFERENCES

Curtiss, J., L. Rodriguez-Uribe, J. McD. Stewart & J. Zhang. 2011. Identification of differentially expressed genes associated with semigamy in Pima cotton (Gossypium barbadense L.) through comparative microarray analysis. BMC Plant Biology 11: 49.

Wendel, J. F., C. L. Brubaker & T. Seelanan. 2010. The origin and evolution of Gossypium. In: Stewart, J. McD., D. Oosterhuis, J. J. Heitholt & J. R. Mauney (eds) Physiology of Cotton pp. 1-18. Springer.

The Range of Lotus

For today's post, I'll be focusing on the lotus. And having said that, how many of you instantly thought of something like this:

To which I can only say: you should be ashamed of yourself. That is not a lotus, that is some wierd aquatic poppy-type thing called Nelumbo nucifera. This is a lotus:

Bird's-foot trefoil Lotus corniculatus, from Lyndon's Garden.

To clarify, Lotus is a genus of over a hundred species of herbaceous legumes native mostly to Eurasia and northern Africa, with smaller numbers of species in sub-Saharan Africa and Australia (Kirkbride 1999). About forty or so species have also been assigned to this genus from the Americas (particularly western North America), but all recent analyses have agreed that the New World species are not immediately related to the Old World species (Allan & Porter 2000; Arambarri et al. 2005) and they have been reclassified as genera Hosackia, Acmispon, Ottleya and Syrmatium—we shall not speak of them again. How the name 'lotus' came to be simultaneously applied to two such different plants as pictured above, I couldn't say, but the practice goes back a long time: the elder Pliny was referring to both sweet clover and a water lily as lotus in the first century AD (Kirkbride 1999). He also used the name 'lotus' for jujubes and (possibly) pomegranates, so he evidently had a certain affection for the word.

Greater lotus Lotus uliginosus, photographed by Forest & Kim Starr.

Lotus species are commonly known as trefoils, in reference to the leaves being divided into three leaflets. As it happens, most Lotus species actually have leaves with five leaflets, but two of those are separated from the others by an extended midrib. Pea-shaped flowers are borne in small terminal clusters; these are most commonly yellow, though some species produce red flowers. A few species have gone by the vernacular name of 'bacon and eggs' in reference to their producing flowers which are a combination of the two colours. Seeds are produced in long straight pods, and the appearance of the clustered pods is responsible for another vernacular name, bird's-foot trefoil. In one group of species, commonly separated as a genus Tetragonolobus but phylogenetically nested among other Lotus (Allan & Porter 2000), the pods bear four longitudinal wings. Even excluding the New World species, the exact number of species recognised in Lotus varies between authors, primarily due to disagreement over the appropriate treatment of segregates of the more widespread and variable taxa.

Young pod and flower of asparagus pea Lotus tetragonolobus, from here.
A number of Lotus species, particularly L. corniculatus and the greater lotus L. uliginosus*, are used as pasture legumes and have become established around the world as a result. Though arguably less productive than alternative legumes such as clover, they are often able to tolerate more marginal habitats (particularly waterlogged ground). Some species do contain secondary metabolites that can produce cyanide, but concentrations are not usually high enough to be a concern. The asparagus pea Lotus tetragonolobus (also known as Tetragonolobus purpureus) is grown for more direct human consumption, with the pods being eaten before they reach maturity. The name 'asparagus pea' is supposed to refer to their flavour, but this website expressed the opinion that: "If you have an excessively moist mouth, and are looking for something to suck all the moisture out and leave you all pasty, then asparagus peas are the vegetable for you."

*There seems to be some disagreement out there about whether Lotus uliginosus should be recognised as distinct from L. pedunculatus. Kirkbride (1999) uses L. uliginosus as a distinct taxon.

REFERENCES

Allan, G. J., & J. M. Porter. 2000. Tribal delimitation and phylogenetic relationships of Loteae and Coronilleae (Faboideae: Fabaceae) with special reference to Lotus: evidence from nuclear ribosomal ITS sequences. American Journal of Botany 87 (12): 1871-1881.

Arambarri, A. M., S. A. Stenglein, M. N. Colares & M. C. Novoa. 2005. Taxonomy of the New World species of Lotus (Leguminosae: Loteae). Australian Journal of Botany 53: 797-812.

Kirkbride, J. H., Jr. 1999. Lotus systematics and distribution. In: Trefoil: The Science and Technology of Lotus, pp. 1-20. Crop Science Society of America and American Society of Agronomy.

Lecantheae and/or Elatostemateae

Elatostema umbellatum var. majus, photographed by Michael Becker.

The Elatostemateae is a tribe of plants in the Urticaceae, the family that includes the nettles (Urticaceae in general have been looked at in an earlier post). Elatostemateae are mostly distinguished from other members of the Urticaceae by their generally tripartite perianth in the female flowers and their brush-like stigmas (Friis 1993). There seems to be some conflict over the appropriate name to call this group: Conn & Hadiah (2009) argued for the use of Elatostemateae, but many authors had previously called this group the Lecantheae. The argument hinges purely on a question of priority a bit too tedious to examine here.

Lecanthus peduncularis, photographed by Li-Chieh Pan.

The question may or may not be moot, anyway. Recent phylogenetic analyses of the Urticaceae have generally agreed that the Elatostemateae can be divided between two clades, one including the genus Elatostema and the other the genera Lecanthus and Pilea. The two groups are morphologically as well as molecularly distinguishable: species of Pilea and Lecanthus generally have opposite leaves, but in Elatostema one of each leaf pair has been greatly reduced (or lost) so that the leaves appear alternate. However, it is currently uncertain whether these two groups together form an exclusive clade. In the analyses by Hadiah et al. (2008), trnL-F sequence data was consistent with a monophyletic Elatostemateae, but rbcL data placed the Lecanthus-Pilea group closer to the tribe Urticeae than to Elatostema. This is not inherently unreasonable: as members of the Urticeae also have brush-like stigmas like those of Elatostemateae, the main distinction between the two tribes is the plesiomorphic absence in the latter of the stinging hairs that characterise the Urticeae.

Pilea fairchildiana, previously Sarcopilea domingensis, from Javier Francisco-Ortega.

Whether monophyletic or not, the Elatostemateae are mostly a tropical and subtropical group. They are mostly herbs and subshrubs, with a smaller number of shrub species. The centre of diversity is in the Old World; only the genus Pilea is found in the Americas. Members of the Elatostema group may be either all included in a single genus or divided between genera Elatostema, Procris and Pellionia distinguished by inflorescence characters. Pilea, the largest genus in the group, includes species in both the Old and New Worlds, of which some are commonly succulent. The Hispaniolan species Pilea fairchildiana has developed a rosulate growth form, remarkably similar to members of genera in the unrelated family Crassulaceae, such as Aeonium and Sempervivum. Until very recently, this species was considered distinctive enough to be placed in a separate genus Sarcopilea; Jestrow et al. (2012) demonstrated its more nested position. Economic usages of Lecantheae species are few: the leaves of some Pilea species, such as the artillery plants* P. microphylla and P. melastomoides, have some limited use as aromatic herbs, while some species of the Elatostema group are apparently used in Indonesia as shampoo.

*The name 'artillery plant' apparently refers to the way in while the male flowers fire forth their pollen, which is supposed to resemble gunsmoke.

REFERENCES

Conn, B. J., & J. T. Hadiah. 2008. Nomenclature of tribes within the Urticaceae. Kew Bulletin 64; 349-352.

Friis, I. 1993. Urticaceae. In: Kubitzki, K., J. G. Rohwer & V. Bittrich (eds) The Families and Genera of Vascular Plants vol. 2. Flowering Plants. Dicotyledons. Magnoliid, hamamelid and caryophylliid families pp. 612-629. Springer.

Hadiah, J. T., B. J. Conn & C. J. Quinn. 2008. Infra-familial phylogeny of Urticaceae, using chloroplast sequence data. Australian Systematic Botany 21: 375-385.

Jestrow, B., J. J. Valdés, F. Jiménez Rodríguez & J. Francisco-Ortega. 2012. Phylogenetic placement of the Dominican Republic endemic genus Sarcopilea (Urticaceae). Taxon 61 (3): 592-600.