Desmodium Desv.

Scientific Description

Family Papilionaceae. Desmodieae.

Habit and leaf form. Shrubs, or herbs. Plants unarmed. Annual (herbs and some shrubs), or perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.2–3 m high (habit variable). Mesophytic, or xerophytic. Leaves small to large; not fasciculate; alternate; spiral; ‘herbaceous’, or leathery; not imbricate; petiolate. Petioles wingless. Leaves non-sheathing; compound; pulvinate; unifoliolate, or ternate. Leaves when trifoliolate, pinnately trifoliolate, or palmately trifoliolate. Leaflets 1, or 3. Lateral leaflets opposite. Leaflets stipellate; pulvinate, or epulvinate; flat, or folded; without lateral lobes. Leaf blades dorsiventral; cross-venulate. Leaves with stipules. Stipules intrapetiolar; free of one another, or concrescent (often, usually leaf-opposed); more or less ochreate (sometimes?), or not ochreate; striate, attenuate; persistent. Leaf blade margins entire (sometimes undulate); flat. Leaves without a persistent basal meristem. Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening absent, or developing from a conventional cambial ring.

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

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes, or in umbels, or in fascicles. Inflorescences compound (two or more flowers per bract axil, often each subtended by a secondary bract as well). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary. Flowers pedicellate; bracteate. Bracts persistent, or deciduous (similar to the stipules). Flowers bracteolate, or ebracteolate; minute to small; very irregular; zygomorphic; not resupinate. The floral asymmetry involving the perianth, or involving the perianth and involving the androecium. Flowers papilionaceous (imbricate-descending, with the posterior petal outside and forming the ‘standard’); basically 5 merous. Floral receptacle with neither androphore nor gynophore. Free hypanthium present, or absent. Hypogynous disk absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; 4–5 lobed. Calyx lobes markedly shorter than the tube to markedly longer than the tube. Calyx imbricate, or valvate; exceeded by the corolla; bilabiate (the posterior pair of members connate for all or much of their length); non-fleshy; persistent; non-accrescent; with the median member anterior. Epicalyx absent. Corolla present; 5; 1 -whorled; appendiculate (the keel petals usually auriculate), or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 4 of the petals joined (the two ventral petals connivent and often apically cohering to form the ‘keel’, and the wings usually more or less adhering to the keel). The joined petals of the papilionate corolla anterior (and sometimes lateral). The wings of the corolla adherent to the keel (nearly always?); not laterally spurred. Standard ‘normally’ developed; not sericeous. Keel not long-acuminate/beaked (blunt, usually usually incurved); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); white, or pink to purple; deciduous; non-accrescent. Petals clawed (but the standard only shortly so). Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; markedly unequal (the filaments alternately long and short); coherent (basally, into a tube); 1 - adelphous, or 2 - adelphous (the tube partially or completely split, and the vexillary stamen either free, or connate less high). 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 (but near the base); versatile; dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Pollen shed as single grains (tricolporate). Fertile gynoecium present. 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-) curved, or bent. Style hairy but not bearded (hairy towards the base only), or glabrous. Stigmatic tissue terminal. Carpel (1–)2–8 ovuled. Placentation marginal. Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile. Ovary summit hairy, the hairs not confined to radiating bands (usually). Stigmas capitate. Ovules pendulous to ascending; biseriate; arillate, or non-arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit sessile; non-fleshy; hairy, or not hairy; not spinose. The fruiting carpel indehiscent, or dehiscent (in that the articles sometimes dehisce along the lower suture); a loment. Pods somewhat elongated, or much elongated; not triangular; straight, or curved; not becoming inflated; more or less flat, or somewhat compressed; regularly constricted between adjacent seeds (usually more deeply so on one side); transversely septate between the seeds, or not transversely septate; wingless. Fruit 1 celled; (1–)2–8 seeded. Seeds reniform; endospermic, or non-endospermic; not mucous; strongly compressed; small; non-arillate. Cotyledons 2; accumbent. Embryo curved, or bent (the radicle inflexed). Testa non-operculate. Micropyle zigzag, or not zigzag. Seedling. Germination phanerocotylar, or cryptocotylar.

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

Geography, cytology, number of species. Native of Australia. 2n=(20), 22. A genus of about 300 species; 12 species in Western Australia.