Lotus (genus)


Lotus, a latinization of Greek lōtos, is a genus of flowering plants that includes most bird's-foot trefoils and deervetches. Depending on the taxonomic authority, roughly between 70 and 150 species are accepted, all legumes; American species formerly placed in the genus have been transferred to other genera. Lotus species are found in the Eastern Hemisphere and adapted to a wide range of habitats.
The aquatic plant commonly known as the Indian or sacred lotus is Nelumbo nucifera, a species not closely related to Lotus.

Description

Most species have leaves with five leaflets; two of these are at the extreme base of the leaf, with the other three at the tip of a naked midrib. This gives the appearance of a pair of large stipules below a "petiole" bearing a trefoil of three leaflets; in fact, the true stipules are minute, soon falling or withering. Some species have pinnate leaves with up to 15 leaflets. The flowers are in clusters of three to ten together at the apex of a stem with some basal leafy bracts; they are pea-flower shaped, usually vivid yellow, but occasionally orange or red. The seeds develop in three or four straight, strongly diverging pods, which together make a shape reminiscent of the diverging toes of a small bird, leading to the common name "bird's-foot".

Taxonomy

The genus Lotus is taxonomically complex. It has at times been divided into subgenera and split into segregate genera, but with no consistent consensus. P.H. Raven in 1971 is said to have been the first to suggest that the "New World" and "Old World" species did not belong in the same genus. A molecular phylogenetic study in 2000 based on nuclear ribosomal ITS sequences confirmed this view. The Western species have been divided between the genera Hosackia s.str., Ottleya, Acmispon and Syrmatium. A 2006 study, primarily concerned with Eastern Lotus species and hence with limited sampling of the American genera, found that they were all monophyletic. The study also supported the view that Dorycnium and Tetragonolobus are not distinct from Lotus at the generic level. More species were added to the 2006 results in 2008, but did not alter the broad conclusions reached before. Clades were identified within Lotus s.str., some of which were significantly different from the sections into which the genus had been divided. However, resolution was incomplete. The results of the analysis were presented in terms of clades and complexes.

Species

The following species are recognised in the genus Lotus:

Species placed elsewhere

Distribution and habitat

The genus contains many dozens of species distributed in the Eastern Hemisphere, including Africa, Europe, western, southern, and eastern Asia, and Australia and New Guinea. They are adapted to a wide range of habitats, from coastal environments to high elevations.

Ecology

Lotus species are used as food plants by the larvae of some Lepidoptera species.
L. corniculatus is an invasive species in some regions of North America and Australia.

Uses

Several species are cultivated for forage, including L. corniculatus, L. glaber, and L. pedunculatus. They can produce toxic cyanogenic glycosides which can be potentially toxic to livestock, but also produce tannins, which are a beneficial anti-bloating compound.
Species in this genus can fix nitrogen from the air courtesy of their root nodules, making them useful as a cover crop. The nodulating symbionts are Bradyrhizobium and Mesorhizobium bacteria. Scientific research for crop improvement and understanding the general biology of the genus is focused on L. japonicus, which is currently the subject of a full genome sequencing project, and is considered a model organism.
Some species, such as L. berthelotii from the Canary Islands, are grown as ornamental plants.