Lathyrus is a genus of flowering plants in the legume family Fabaceae (subfamily Faboideae, tribe Fabeae), comprising roughly 150 to 180 accepted species of annual and perennial herbs. Members are commonly called peas, peavines, or vetchlings, and many are familiar from gardens, meadows, and woodland edges across the temperate Northern Hemisphere as well as tropical East African and South American highlands.
Most species are climbing or scrambling herbs that pull themselves up through surrounding vegetation using slender tendrils at the tips of their pinnately compound leaves. The stems are often distinctively winged or angled, and the foliage typically consists of a few pairs of leaflets followed by a branching tendril. Flowers are the classic "papilionoid" pea form — a broad standard petal at the back, two wings on the sides, and a fused keel enclosing ten stamens (nine fused, one free) and a slender style that is bent at nearly a right angle. They are borne in elongated racemes, often one to three inches across, in shades of rose, red, maroon, pink, white, yellow, purple, and blue, frequently bicoloured. Fruits are dry, dehiscent pods typical of the pea family.
The genus is centred on temperate Eurasia, with substantial diversity in Asia (around 78 species), Europe (around 52), North America (around 30), and smaller but distinctive radiations of around 24 species each in tropical East Africa and temperate South America. Like other legumes, Lathyrus species form symbiotic associations with nitrogen-fixing root bacteria, making them important contributors to soil fertility in meadows, woodlands, and wetlands.
Several Lathyrus species are economically and culturally important. The sweet pea (L. odoratus) is one of the best-known cottage-garden ornamentals; the everlasting pea (L. latifolius) is a hardy climbing perennial widely grown in temperate gardens; the grass pea (L. sativus) is cultivated as a food and fodder crop; and the tuberous pea (L. tuberosus) has been grown for its starchy tubers. Several species, however, contain a non-protein amino acid (oxalyldiaminopropionic acid, or ODAP) that can cause lathyrism, a serious neurological disease, when their seeds form a large part of the diet.
Etymology
The genus name Lathyrus is taken from Latin botanical usage, where related forms were applied to peas; Linnaeus formalised it in Species Plantarum in 1753. The vernacular English names "pea," "peavine," and "vetchling" all reflect the genus's close kinship with cultivated peas (Pisum) within the tribe Fabeae, and regional names follow similar threads — French "gesse," Italian "cicerchie," German "Erbse," Polish "groszek," Hungarian "lednek," and Slovenian "grahor."
Distribution
Lathyrus has a broadly temperate distribution and is centred in Eurasia. Wikipedia counts roughly 78 species in Asia, 52 in Europe, 30 in North America, and around 24 each in tropical East Africa and temperate South America. Regional floras illustrate the genus's density: 22 species (including subspecies of L. vernus) are documented in Switzerland alone, and the SEINet herbarium consortium catalogues a substantial cohort of species across the southwestern United States, including Arizona and New Mexico.
Ecology
Like other legumes, Lathyrus species form nitrogen-fixing symbioses with soil bacteria, enriching their habitats and supporting roles as pioneer or meadow species. They occupy a wide range of habitats: L. pratensis is a characteristic meadow plant, L. palustris occurs in marshy wetlands, L. sylvestris and L. niger grow in woodlands, and L. vernus shows subspecific variation across alpine and montane forest zones. Larvae of certain Lepidoptera species feed on Lathyrus, and observational studies summarised on Wikipedia suggest that some montane-meadow populations respond negatively to warming temperatures, showing decreased abundance and reduced plant size.
Cultivation
Garden Lathyrus species are best grown in full sun and moderately fertile, well-drained soil with high organic matter, though they tolerate a range of textures from light to heavy and pH from acidic to slightly alkaline. Many species climb 4 to 9 feet via tendrils and spread 1 to 3 feet, making them well suited to cottage-garden trellises, fences, and bank plantings. NC State Extension reports broad winter hardiness across USDA zones 3a–8b. Maintenance is moderate; plants tolerate drought and erosion but are prone to powdery and downy mildew, occasional rust, and pests such as aphids and slugs.
Propagation
The standard route for Lathyrus is seed. Seeds benefit from a 24-hour warm-water pre-soak before being sown in early spring in a cold frame; seedlings are pricked out individually as soon as they are large enough to handle. Seed may also be sown directly outdoors in mid-spring. Spring division of perennial species is possible, but plants do not always re-establish reliably after disturbance and should be handled with care.
Cultural Uses
Several Lathyrus species have long histories as food and fodder. Seeds and young leaves and stems of some species are eaten cooked, and the grass pea (L. sativus) remains an important pulse crop in parts of Asia and Africa; the tuberous pea (L. tuberosus) has been cultivated for its starchy tubers. Many species have also been used as livestock fodder, and the sweet pea (L. odoratus) is one of the most widely grown ornamental annuals.
Taxonomy
Lathyrus L. was established by Linnaeus in Species Plantarum, page 729, in 1753, and it sits in family Fabaceae, subfamily Faboideae, tribe Fabeae alongside the closely related genera Pisum, Vicia, and Lens. Approximate species counts vary by source: Wikipedia cites ~181 accepted species, SEINet ~150, and the GBIF backbone records 422 descendant names (including infraspecific taxa and synonyms). The genus formerly included Orobus as a separate group, now subsumed within Lathyrus.
Toxicity and Lathyrism
Several Lathyrus species — most notoriously the grass pea, L. sativus — contain the neurotoxic non-protein amino acid β-N-oxalyl-L-α,β-diaminopropionic acid (ODAP). When seeds of these species form a large and prolonged part of the diet, especially during famines, they can cause lathyrism, a disease of the nervous system marked by paralysis and convulsions. Toxins are concentrated in the seeds and fruits, and NC State Extension rates overall poison severity as low for typical garden exposure, with serious effects requiring large quantities.
