The Resurrection of Grass

The resurrection grass Oropetium thomaeum, photographed by Diana Margaret Napper.
Even for a grass, the annual Oropetium thomaeum is not a very prepossessing plant. Only a couple of inches in height, it can be found as small tufts in arid or saline habitats in tropical Africa and Asia. In some parts of India, it has been recorded as a dominant grass species, probably because its small size makes it resistant to grazing while, for instance, its somewhat taller perennial relative O. roxburghianum is restricted to growing under shrubs that protect it from hungry ruminants (Gaff & Bole 1986).

Despite its modesty, O. thomaeum is not devoid of interest. It is an example of what is known as a 'resurrection plant', able to survive severe desiccation in a dormant state only to apparently come back to life after rain. Because O. thomaeum is a diploid species with a relatively small genome (one of the smallest of all grasses), it has been touted as potential useful in studying the genetic factors controlling drought tolerance (Bartels & Mattar 2002). According to this article, it has seen some use in attempts to rehabilitate degraded environments. Oropetium thomaeum has also been shown to differ from most plant species in that it is the shoot that emerges first from the germinating seed rather than the root (Dakshini & Tandon 1970).

Oropetium is a small genus of seven species of grasses in the subfamily Chloridoideae, with three species found in India and five in Africa (Phillips 1975). Despite the small number of species, members of Oropetium have been divided between no less than five genera in the past, reflecting a fair degree of disparity in their reproductive morphology. All, however, are relatively small narrow-leaved grasses forming dense tufts. Whether the African species possess the resurrective abilities of the Asian species remains, so far, unknown.

REFERENCES

Bartels, D., & M. Z. M. Mattar. 2002. Oropetium thomaeum: a resurrection grass with a diploid genome. Maydica 47 (3-4): 185-192.

Dakshini, K. M. M., & R. K. Tandon. 1970. An unusual type of germination of graminaceous seed. Annals of Botany 34 (2): 423-425.

Gaff, D. F., & P. V. Bole. 1986. Resurrection grasses in India. Oecologia 71: 159-160.

Phillips, S. M. 1975. A review of the genus Oropetium (Gramineae). Kew Bulletin 30 (3): 467-470.

From Giant Reeds to Tiny Leaves

Giant reed Arundo donax, photographed by Russ Kleinman & Richard Felger.

The grasses are without a doubt one of the most successful groups of plants in the modern environment. So it is only fitting that for today's post I'm going to be looking at one of the subgroups of the grasses, the Arundinoideae.

The Arundinoideae, including the reeds and related species, has been long recognised as a subfamily of grasses, but rather vaguely so. Most of the characters of leaf anatomy previously used to define the group are either plesiomorphies or absences. Arundinoids use the plesiomorphic C₃ photosynthetic pathway rather than the derived C₄ pathway and lack the radiate leaf anatomy associated with C₄ photosynthesis. They also lack the fusoid leaf cells with accessory arm cells that are characteristic of the bamboos. In other features, 'arundinoids' were quite variable, and it therefore came as no surprise to anyone when phylogenetic analyses indicated that the group was polyphyletic. As a result, the Grass Phylogeny Working Group (2001) divided the arundinoids between a number of subfamilies, separating the wiregrasses as the Aristidoideae and the oatgrasses and pampas grasses as the Danthonioideae. This reduced the Arundinoideae proper, previously including well over 600 species, to less than 40.

Common reed Phragmites australis, from here.

Even so, the arundinoids remain a disparate group, and morphological synapomorphies of the group remain elusive. The taxonomic core of the group, the reeds of the genera Arundo, Phragmites and Molinia, are connected by the possession of hollow culm internodes, a punctiform hilum (the detachment scar on the 'seed') and convex adaxial rib sides in the leaf blade (Grass Phylogeny Working Group 2001), but these features are not shared by all other arundinoids. The reeds are found in damp habitats, and the common reed Phragmites australis can grow in standing water. The largest species, the giant reed Arundo donax, can reach a height of ten metres under ideal growth conditions. In contrast, the Tom Thumb grass Dregeochloa pumila is found in the Namib Desert of South Africa and Namibia, and doesn't reach any higher than 25 mm (excluding the flower stalk, which may give it another inch or so). Dregechloa pumila is also remarkable as the only succulent species of grass. Also included in the Arundinoideae are the crinipoid grasses, a somewhat poorly known assemblage of species found in highlands of Africa, Madagascar and southern India (Linder et al. 1997).

Tom Thumb grass Dregechloa pumila, from Ernst van Jaarsveld.

Arundo donax has become known in some areas as an agressive weed, particularly in the US. It has one of the fastest growth rates of any plant, potentially up to ten centimetres in a single day (remember, that's four Dregeochloas!) Despite its invasive potential, some have been promoting it as a potential crop species, particularly for the biofuel market (presenting its fast growth rate as an outright advantage). Arundo donax is also the preferred material for woodwind reeds. Phragmites australis (also a problematic weed in the wrong circumstances) has been used in wastewater purification, and Wikipedia also notes that it is edible, quoting that the young stems "while still green and fleshy, can be dried and pounded into a fine powder, which when moistened is roasted like marshmallows". 'Like' marshmallows, perhaps, but I don't think that I'll be rushing to make the substitution.

REFERENCES

Grass Phylogeny Working Group. 2001. Phylogeny and subfamilial classification of the grasses (Poaceae). Annals of the Missouri Botanical Garden 88 (3): 373-457.

Linder, H. P., G. A. Verboom & N. P. Barker. 1997. Phylogeny and evolution in the Crinipes group of grasses (Arundinoideae: Poaceae). Kew Bulletin 52 (1): 91-110.

Peeling the Lily

The toad lily Tricyrtis hirta. Photo by André Karwath.

Pity the poor Liliaceae. At one time, the family stood as the repository for almost all monocots with large-petaled flowers except orchids. Over the years, successive reclassifications have steadily whittled it down until the current Liliaceae is left with a mere ten to sixteen or so genera (depending on whether or not the Calochortaceae are treated as a separate family) found in the Holarctic region. Of course, these genera still include such luminaries as Lilium (lilies) and Tulipa (tulips), so even in its minority the Liliaceae can still draw its share of attention.


Greig's tulip Tulipa greigii growing wild in Kazakhstan. Photo by Rustem Vagapov. I have to admit that the thought of such horticultural wonders as tulips and orchids growing wild has always been a strange one to me.

Molecular studies of the Liliaceae have agreed on the monophyly of Liliaceae sensu stricto (excluding 'Calochortaceae') but differ on the relationships of the 'Calochortaceae', whether a monophyletic sister to Liliaceae s. s. (Patterson & Givnish 2002) or paraphyletic to the latter (Rønsted et al., 2005). Within Liliaceae s. s., there is a well-supported division between the Lilioideae and a small clade Medeoloideae. Whatever the phylogeny, it seems likely that the ancestor of the Liliaceae in the broad sense was a shade-loving, rhizomatous plant with broad reticulate leaves, as is characteristic of Medeoloideae and 'Calochortaceae' other than Calochortus (Patterson & Givnish 2002). Calochortus and Lilioideae independently became adapted to more open habitats, developing narrower leaves and bulbs instead of rhizomes (hence a more seasonal growing cycle). Both lineages also developed more showy flowers than their relatives (showy flowers are also found in the genus Tricyrtis, which may or may not be closely related to Calochortus) and replaced the berries of their ancestors with dehiscent capsules, so that their seeds became dispersed by wind instead of by animals. Again, capsules are also found in Tricyrtis, as well as in the genus Scoliopus that has distinctive fleshy capsules that are believed to encourage seed dispersal by ants (Patterson & Givnish 2002).


The Indian cucumber (because of its edible rhizome) Medeola virginiana, a North American representative of the forest-dwelling Medeloideae. Photo by David Smith.

As well as reproducing by seeds, some Liliaceae also reproduce asexually. A number of bulbiferous species produce bulbils, small lateral offshoots of the bulb. These may break off and grow into new plants elsewhere, generally when carried by the action of burrowing animals such as moles and mole-rats.

REFERENCES

Patterson, T. B., & T. J. Givnish. 2002. Phylogeny, concerted convergence, and phylogenetic niche conservatism in the core Liliales: insights from rbcL and ndhF sequence data. Evolution 56 (2): 233-252.

Rønsted, N., S. Law, H. Thornton, M. F. Fay & M. W. Chase. 2005. Molecular phylogenetic evidence for the monophyly of Fritillaria and Lilium (Liliaceae; Liliales) and the infrageneric classification of Fritillaria. Molecular Phylogenetics and Evolution 35: 509-527.