Lotus L. is a genus of roughly 70–150 species of annual and perennial herbs and subshrubs in the legume family Fabaceae, placed in tribe Loteae. The genus was established by Carl Linnaeus in 1753 in his Species Plantarum. Common names include bird's-foot trefoils, deervetches, and — for the vivid yellow-flowered species — bacon-and-eggs.
Plants in the genus are recognizable by their pinnate leaves, which typically bear five leaflets arranged with two basal stipular leaflets flanking the stem and three terminal leaflets at the tip of a naked midrib. Flowers are characteristic papilionoid blooms, most often bright yellow but occasionally orange or red, held in clusters of three to ten on slender peduncles. The distinctive seedpods are straight and strongly diverging, resembling bird's toes radiating from a central point — the feature that gave rise to the most familiar common name.
Lotus species occur predominantly across the Eastern Hemisphere, with native distributions spanning Europe, Africa, western, southern and eastern Asia, Australia, and New Guinea. They colonize a wide range of habitats, from coastal cliffs and sand dunes to alpine meadows and rocky hillsides. Like most legumes, species in Lotus form root-nodule symbioses with nitrogen-fixing bacteria (Bradyrhizobium and Mesorhizobium), enriching the soils in which they grow.
Several species are economically important as forage plants: L. corniculatus (common bird's-foot trefoil), L. pedunculatus (greater bird's-foot trefoil), and L. glaber are widely sown in temperate grasslands and pastures. Their condensed tannins inhibit the rumen bloat that afflicts livestock grazing many other legumes, though cyanogenic glycosides present in the foliage can be toxic at high intake levels. L. japonicus has emerged as a model organism in legume biology and is the subject of a complete genome sequencing project. The ornamental L. berthelotii, native to the Canary Islands, is prized for its coral-red flowers and trailing habit.
The taxonomy of the genus has been substantially revised by molecular phylogenetic work conducted between 2000 and 2008, which demonstrated that the American species previously included in Lotus belong in separate genera — principally Hosackia, Acmispon, Ottleya, and Syrmatium. Under the current, predominantly Eastern Hemisphere circumscription, Dorycnium and Tetragonolobus are retained within Lotus.
Etymology
The genus name Lotus is a latinization of the ancient Greek word lōtos (λωτός), which was applied in antiquity to a range of unrelated plants. Linnaeus adopted the name when he formally described the genus in Species Plantarum (1753). The genus is entirely unrelated to the aquatic sacred lotus (Nelumbo nucifera, family Nelumbonaceae) or to water lilies (Nymphaea), despite sharing the same classical root name.
Distribution
The core native range of Lotus encompasses the Eastern Hemisphere: Europe (from the Atlantic coasts to the Caucasus and central Asia), Africa (including the Canary and Madeira islands), western, southern, and eastern Asia, Australia, and New Guinea. Species occupy a broad ecological amplitude — coastal dunes and cliffs, Mediterranean garrigue, temperate meadows, sub-alpine and alpine grasslands. In Switzerland, the genus is represented by L. alpinus, L. corniculatus and its aggregate, L. maritimus, L. pedunculatus, and L. tenuis. In North America, where species occur largely as introductions, L. corniculatus is now widespread as an escapee from forage cultivation and is considered invasive in parts of the continent and in Australia.
Taxonomy
Lotus L. was described by Linnaeus in 1753 (Sp. Pl.: 773) and placed in family Fabaceae, tribe Loteae. The number of accepted species has been contested, with estimates ranging from about 70 to 150, partly reflecting ongoing revisions following molecular phylogenetic work. Studies published between 2000 and 2008 showed that New World species traditionally included in Lotus form separate, well-supported clades, leading to their segregation into Hosackia, Acmispon, Ottleya, and Syrmatium. The current Lotus s.str. is predominantly an Eastern Hemisphere genus. Within it, Dorycnium (a group of Mediterranean subshrubs) and Tetragonolobus (the winged peas) are now subsumed. GBIF records 325 descendant taxa; ITIS recognizes the genus under the same Linnaean authorship. Regional floras such as SEINet still reflect the broader pre-revision circumscription of roughly 100 species.
Ecology
Lotus species are important components of temperate grassland and meadow communities. They are obligate light-demanders, thriving in open, often nutrient-poor habitats on a wide range of soil textures and tolerating pH from acidic to mildly alkaline. The genus forms nitrogen-fixing root-nodule symbioses with rhizobial bacteria (Bradyrhizobium and Mesorhizobium), contributing fixed nitrogen to the soil and enabling colonization of impoverished substrates. Species serve as larval food plants for a range of Lepidoptera, and the flowers attract bees and other pollinators. L. corniculatus in particular is a key nectar source in temperate grassland pollinator networks.
Cultivation
Several Lotus species have long been cultivated as forage legumes. L. corniculatus and L. pedunculatus are sown widely in temperate pastures because their condensed tannins prevent the rumen bloat that can be fatal to cattle and sheep grazing other legumes such as clover. However, all parts of the plants contain cyanogenic glycosides, and high intake can be toxic to livestock. L. glaber is similarly used in drier pastoral systems. In gardens, L. berthelotii (parrot's beak) from the Canary Islands is grown as a trailing ornamental for its narrow silver foliage and vividly coloured red-orange flowers. L. japonicus has become the primary model legume in genetic and genomic research — its compact genome and tractability for transformation make it analogous in the legume world to Arabidopsis in general plant biology.
Propagation
Propagation of Lotus species from seed is the primary method. Seeds benefit from scarification or soaking in warm water for 24 hours prior to sowing, as the seed coat can be impermeable. Spring or autumn sowing is recommended; germination occurs within two to four weeks at around 15 °C. For small quantities, seeds can be started in pots under cold frames and transplanted to individual containers before being planted out in late spring. As nitrogen-fixing legumes, established plants do not require nitrogen fertilization and perform well on lean, well-drained soils in full sun.
Cultural Uses
In traditional and folk medicine, L. corniculatus has been used to treat inflammation, spasms, fever, and digestive ailments. Flowers have been attributed antispasmodic, cardiotonic, and sedative properties, and roots have been used as a carminative and tonic. The flowers yield an orange-yellow dye. Young seedpods have occasionally been eaten raw, though caution is warranted given the presence of cyanogenic glycosides throughout the plant.
