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.