Dicerma DC.

Scientific Description

Family Papilionaceae. Desmodieae.

Sometimes included in Desmodium.

Habit and leaf form. Multistemmed sub- shrubs, or herbs. Plants unarmed. Annual. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.2–1.5 m high (sometimes prostrate). Mesophytic. Leaves small to medium-sized; not fasciculate; alternate; spiral; ‘herbaceous’, or leathery; not imbricate; petiolate. Petioles wingless. Leaves non-sheathing; compound; pulvinate; ternate. Leaves palmately trifoliolate (‘almost’ or ‘apparently’ digitate). 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; concrescent (amplexicaul, 3–4 lobed); more or less ochreate, or not ochreate (the rachis arising from the open side of the ‘tube’); persistent. Leaf blade margins entire (sometimes undulate); flat. Leaves without a persistent basal meristem. Leaf anatomy. Glandular hairs present (interspersed with hooked hairs). Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening developing from a conventional cambial ring.

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

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes. Inflorescences compound (two or three flowers per bract axil, each subtended by secondary bracts as well). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal and axillary; linear, compact ‘racemes’, to 17 cm long, the flowers obscured by bracts and bracteoles. Flowers pedicellate. Pedicels flattened. Flowers bracteate. Bracts persistent (subulate). Flowers (bi-) bracteolate. Bracteoles persistent (subulate, subtending the calyx). Flowers 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 present; intrastaminal; annular. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; 4–5 lobed. Calyx lobes about the same length as 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, or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the two ventral petals connivent and often apically cohering to form the ‘keel’). The joined petals anterior. The wings of the corolla more or less free from the keel (‘scarcely adhering’); not laterally spurred. Standard ‘normally’ developed (erect); not sericeous. Keel about equalling the wings (straight); not long-acuminate/beaked; neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); cream, or pink to purple (or mauve); deciduous; non-accrescent. Petals clawed (the wings and keel long clawed, 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 (the tube partially split adaxially, the vexillary stamen being 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 2 ovuled. Placentation marginal. Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile. Ovary summit hairy, the hairs not confined to radiating bands (densely hirsute). 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; densely hairy; not spinose. The fruiting carpel indehiscent; a loment (with only (1–)2 ‘articles’). Pods somewhat elongated, or much elongated; not triangular; straight; not becoming inflated; more or less flat, or somewhat compressed; regularly constricted between adjacent seeds (with both margins deeply indented); transversely septate between the seeds, or not transversely septate; wingless. Fruit 1 celled; (1–)2 seeded. Seeds lenticular; endospermic, or non-endospermic; not mucous; compressed (lenticular); 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 1 species; 1 species in Western Australia.