Field of Science

Acervulinids: Reef Forams

Regular readers of this site will know that, contrary to common belief, not all representatives of the vaguely defined category of organisms known as 'protozoa' are too small to be seen with the naked eye. Some are very visible indeed, and many of the more visible forms can be found among the shell-constructing amoeboids known as Foraminifera. One group of giant forams, the xenophyophores, has become fairly famous in internet circles as one of the contenders for the title of 'largest single cell', though, as noted in the post linked to, the question is kind of a pointless one with regard to forams. Besides, as described later in this post, xenophyophores may not have even have always been the largest forams.

Encrusting nodules of Acervulina inhaerens from Rhodes, from M. Hesemann.

The Acervulinidae are a family of reef-inhabiting forams belonging among the rotaliids. Juvenile chambers of newly growing acervulinids are arranged in a flat spiral, but chambers of mature specimens may be arranged in one to several layers. The chambers do not have regular apertures, and instead their walls are only pierced by coarse pores (Perrin 1994). Genera and species of acervulinids are distinguished by the presence, arrangement and shapes of layers and chambers, but defining distinctions appropriately is challenging. Acervulinids do not have a determinate 'adult morphology'; instead, the final adult appearance can be affected by factors such as substrate relief and water movement. Properly identifying acervulinids therefore requires identification of features independent of these external factors.

Living crust of Gypsina plana, photographed by Hal Ray Tichenor.

Acervulinids can be abundant on tropical coral reefs, and may play a not insiginificant role in reef formation as binding organisms. They tend to be particularly prominent in deeper parts of the reef, as they can tolerate lower light levels than other organisms such as coralline algae; in shallower parts of the reef, they are found in more cryptic locations among the coral. Acervulinids may be free-living, or they may be directly attached to their substrate. Like the star-shaped calcarinids, their primary food source is benthic diatoms (that they may or may not live with symbiotically), and the abrupt disappearance of the modern Acervulina inhaerens below depths of 130 m probably corresponds to the lower limit of that food source (Bosellini & Papazzoni 2003).

Fossilised nodules from a Solenomeris reef, photographed by Stefano Dominici. Note that Stefano identifies these as Acervulina; due to the complications in distinguishing acervulinid taxa, it remains contentious whether Solenomeris and Acervulina can be reliably separated.

Attached acervulinids may form either nodules or spreading crusts, depending on species and/or growth conditions (Perrin 1994). Such nodules or crusts may have diameters in the millimetre range, but some living species may be within the decimetre range. The most dramatic expression of acervulinid potential, however, was known from the Tethyan region during the Eocene period (the Tethys, for those unfamiliar with it, was the sea that connected the Atlantic and Indian Oceans north of Africa, before the northward movement of that continent closed off the Mediterranean at the eastern end). Here was found Solenomeris ogormani, initially interpreted as a red alga but since reidentified as an acervulinid. Solenomeris was primarily an encrusting form, but large growths would also produce tightly packed branches one or two centimetres in diameter. Over time, Solenomeris formed massive metre-sized domes, and these domes together would form entire reefs stretching over multiple kilometres: reefs formed not of coral, or of algae, but purely of forams!


Bosellini, F. R., & C. A. Papazzoni. 2003. Palaeoecological significance of coral−encrusting foraminiferan associations: a case−study from the Upper Eocene of northern Italy. Acta Palaeontologica Polonica 48 (2): 279-292.

Perrin, C. 1994. Morphology of encrusting and free living acervulinid Foraminifera: Acervulina, Gypsina and Solenomeris. Palaeontology 37 (2): 425-458.

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.


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.

The Parulidae: Not-warblers, Not-ovenbirds and Not-redstarts

Black-crested warbler Myiothlypis nigrocristata, photographed by Mikko Pyhälä.

There is no denying the current status of English as the de facto lingua franca of the world*. And yet, I feel that a complaint must be laid at the feet of the Brits: they're a bit unimaginative when it comes to animal names. Many a British explorer, upon being presented with some hitherto unfamiliar product of the natural world, proceeded to label it with the name of whatever inhabitant of his native Europe he felt bore some vague resemblance. And hence, even today, there are significant groups of animals such as the Parulidae that are almost without a vernacular name to genuinely call their own.

*The potential irony of this sentence is not lost on me.

The Parulidae are a family of birds found throughout the Americas, though in the northern United States and Canada they are represented by migratory species that retreat further south in the cold months. Many of the migratory species have males with brightly coloured breeding plumage and are consequently idolised by North American bird watchers; non-migratory species, on the other hand, tend to have similarly subdued males and females (Update: see comments below). Members of the Parulidae are generally referred to as 'warblers' or 'wood warblers', despite not being at all closely related to the European warblers. Instead, parulids are members of the 'nine-primaried oscines', the passerine clade that also includes such birds as finches, buntings, sparrows, cardinals and tanagers. Within the nine-primaried oscines, parulids are closely related to the Icteridae, another American clade containing its fair share of representatives doomed to masquerade under stolen names (Barker et al. 2013).

Ovenbird Seiurus aurocapilla on its nest, photographed by M. C. Donald.

Though the nine-primaried oscines as a whole are fairly stable in their membership, recent years have seen a fair bit of shuffling back and forth between the clade's constituent families. As a result of this shuffling, the name 'Parulidae' has come to be associated with a core clade that excludes a number of more uncertainly placed taxa previously included in the family, such as the Central American wrenthrush Zeledonia coronata. A recent comprehensive study of the molecular phylogeny of the core parulids by Lovette et al. (2010) also resulted in a proposed shifting of many generic boundaries within the clade. According to Lovette et al., the basalmost member of the Parulidae is the ovenbird Seiurus aurocapilla, a migratory but monomorphic, relatively large parulid of North and Central America. Just to confuse matters, the name 'ovenbird' has also been used for an unrelated group of South American birds of the genus Furnarius. To be charitable, this is not a case of inappropriate name-saking, but refers to the construction by both groups of domed nests resembling an old earthernware oven. The next member of the parulids to split off was the worm-eating warbler Helmitheros vermivorus, a relatively long-billed species that migrates between the eastern United States and Central America.

Swainson's warbler Limnothlypis swainsonii, photographed by Greg Lavaty.

Next comes a clade of eight species classified in the genera Parkesia, Vermivora, Mniotilta, Limnothlypis and Protonotaria. The black-and-white warbler Mniotilta varia is noted for its distinctive feeding behaviour: it crawls along branches like a nuthatch or creeper, gleaning insects from the bark. The prothonotary warbler Protonotaria citrea is a bright yellow species that Kurt Vonnegut devoted some time to in Jailbird: "The song of a prothonotary warbler is notoriously monotonous, as I am the first to admit...Still—they are capable of expressing heartbreak—within strict limits, of course" (I personally feel the same about skylarks). The waterthrushes of the genus Parkesia are larger, terrestrially-feeding species.

Chestnut-sided warbler Setophaga pensylvanica, photographed by Cephas.

Other North American species are placed by Lovette et al. in the larger genera Geothlypis, Oreothlypis and Setophaga. The last genus contains the species previously included in Dendroica, but the recognition that the American redstart Setophaga ruticilla (again, no relation to the European redstart) is nested within Dendroica leads to the use of the older name. These genera include some of the most colorful parulids. The remaining genera Myiothlypis, Basileuterus, Cardellina and Myioborus form a mostly Neotropical clade. Myioborus species are also known as redstarts, presumably by comparison with the European birds as not one of them actually possesses a red tail. The name 'whitestart' has supposedly been proposed instead, but the only time that name appears to see use is when it is referred to by someone explaining why they are not using it...


Barker, K. F., K. J. Burns, J. Klicka, S. M. Lanyon & I. J. Lovette. 2013. Going to extremes: contrasting rates of diversification in a recent radiation of New World passerine birds. Systematic Biology 62 (2): 298-320.

Lovette, I. J., J. L. Pérez-Emán, J. P. Sullivan, R. C. Banks, I. Fiorentino, S. Córdoba-Córdoba, M. Echeverry-Galvis, F. K. Barker, K. J. Burns, J. Klicka, S. M. Lanyon & E. Bermingham. 2010. A comprehensive multilocus phylogeny for the wood-warblers and a revised classification of the Parulidae (Aves). Molecular Phylogenetics and Evolution 57: 753-770.