Lathyrus L.

Scientific Description

Family Papilionaceae. Vicieae.

Habit and leaf form. Ours glabrous herbaceous climbers; not resinous. ‘Normal’ plants to switch-plants (leaves well developed but reduced to two leaflets, and green winged stems). Plants unarmed. Annual. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems winged. To 3 m long. Climbing; tendril climbers. Tendrils branched (terminating the leaves). Mesophytic. Leaves medium-sized; alternate; distichous; ‘herbaceous’; not imbricate; petiolate. Petioles winged to wingless (angular to narrowly winged). Leaves non-sheathing; compound; epulvinate; in ours, bifoliolate. Leaflets 2; 2–4.5 cm long. Lateral leaflets opposite. Leaflets not stipellate; pulvinate, or epulvinate; elliptic, or oblong, or ovate, or obovate; sessile; flat, or rolled (ptyxis supervolute); without lateral lobes. Leaflet margins flat. Leaf blades dorsiventral. Leaves conspicuously with stipules. Stipules intrapetiolar; adnate to the petiole, or free of the petiole; free of one another; leafy (half sagittate); persistent. Leaf blade margins entire. Leaves without a persistent basal meristem. Stem anatomy. Secondary thickening absent, or anomalous.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; (1–)2(–3) per axil. Inflorescences axillary; mostly two-flowered, long-pedunculate axillary racemes. Flowers pedicellate; bracteate. Bracts deciduous (small, caducous). Flowers ebracteolate; medium-sized (showy); odourless; very irregular; zygomorphic. The floral asymmetry involving the perianth and involving the androecium. Flowers papilionaceous (imbricate-descending, with the posterior petal outside and forming the ‘standard’); 5 merous. Floral receptacle developing a gynophore to with neither androphore nor gynophore. Free hypanthium present, or absent. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; five lobed. Calyx lobes markedly shorter than the tube. Calyx glabrous; imbricate, or valvate; exceeded by the corolla; regular, or bilabiate; persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate, or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the two ventral petals connivent to form the ‘keel’), or 4 of the petals joined (with the wings adherent to the keel). The joined petals of the papilionate corolla anterior (or anterior and lateral). The wings of the corolla adherent to the keel, or free from the keel; not laterally spurred. Standard ‘normally’ developed (much larger than the wings and keel); not sericeous. Keel conspicuously exceeded by the wings (incurved); not long-acuminate/beaked (blunt); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); red and purple, or pink and purple (usually standard purple, wings and keel red); deciduous. Petals clawed. Fertile stamens present. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal to markedly unequal; coherent (the filaments basally connate into a truncate, scarcely oblique tube); 2 - adelphous (9+1, with the tenth, posterior stamen free). The staminal tube free from the keel petals. Androecial members 1 -whorled (although diplostemonous). Androecium exclusively of fertile stamens. Stamens 10; all more or less similar in shape; diplostemonous; both opposite and alternating with the corolla members. Anthers separate from one another, or connivent; all alike; dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 1 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium monomerous; of one carpel; superior. Carpel stylate; apically stigmatic. Style (in-) bent. Style flattened (dorsally). Style bearded down one side (adaxially). Stigmatic tissue terminal. Carpel 6–15 ovuled. Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary subsessile to stipitate. Ovules pendulous to ascending; biseriate; arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit 60–100 mm long; subsessile to sessile; non-fleshy; not hairy (glabrous); not spinose. The fruiting carpel dehiscent; a legume. Pods much elongated (narrowly oblong); not triangular; straight; not becoming inflated; more or less flat; not constricted between the seeds; not transversely septate; wingless. Valves of the dehisced pod twisted, or not twisted. Fruit 1 celled. Dispersal unit the seed. Fruit in ours, (5–)6–8(–9) seeded. Seeds oblong; non-endospermic; not mucous; compressed; small to medium sized; arillate. Cotyledons 2; accumbent. Embryo chlorophyllous; curved, or bent. Testa non-operculate; conspicuously colour-patterned. Micropyle zigzag, or not zigzag. Seedling. Germination cryptocotylar.

Physiology, biochemistry. Nitrogen-fixing root nodules present. Aluminium accumulation not found. Photosynthetic pathway: C₃.

Geography, cytology, number of species. Adventive. 2n=14. A genus of about 150 species; 2 species in Western Australia.

Additional comments. This description omits variation not applicable to L. tingitanus.