Medicago L.

Scientific Description

Family Papilionaceae. Trifolieae.

Habit and leaf form. Herbs; not resinous. Annual, or perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.4–1 m high. Helophytic, or mesophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; not imbricate; petiolate; non-sheathing; not gland-dotted; aromatic, or without marked odour; compound; epulvinate; ternate. Leaves pinnately trifoliolate. Leaves imparipinnate. Leaflets 3; not stipellate; pulvinate, or epulvinate; flat. Leaf blades dorsiventral. Leaves with stipules. Stipules intrapetiolar; adnate to the petiole; free of one another, or concrescent; scaly, or leafy; persistent. Leaf blade margins minutely dentate (denticulate). 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 self pollinating). Pollination mechanism conspicuously specialized (involving an explosive tripping mechanism).

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’ (mostly); when solitary, axillary; in racemes, or in heads. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences axillary; axillary few-flowered racemes, sometimes reduced to one flower. Flowers shortly pedicellate; bracteate (usually), or ebracteate; ebracteolate; small; very irregular; zygomorphic; not resupinate. The floral asymmetry 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 developing a gynophore, or with neither androphore nor gynophore. Free hypanthium 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 imbricate, or valvate; exceeded by the corolla; campanulate; regular to unequal but not bilabiate (with five subequal lobes); non-fleshy; persistent; non-accrescent; with the median member anterior. Epicalyx absent. Corolla present; 5; 1 -whorled; appendiculate (at the bases of the wings). Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the two ventral petals connivent to form the ‘keel’). The joined petals anterior. The wings of the corolla free from the keel; laterally spurred (each with a short, rounded lobe having a hornlike protusion resting against a groove of the keel). Standard ‘normally’ developed; emarginate. Keel conspicuously exceeded by the wings; not long-acuminate/beaked (blunt); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); yellow, or purple, or violet, or blue; deciduous. Petals clawed. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal, or markedly unequal; coherent (nine of them with filaments basally united to form an adaxially split tube); 2 - adelphous (1+9, the vexillary member free of the tube); 1 -whorled. Androecium exclusively of fertile stamens. Stamens 10; all more or less similar in shape, or distinctly dissimilar in shape; (sub-) diplostemonous; both opposite and alternating with the corolla members. Filaments filiform (i.e., beyond the tube). Anthers separate from one another, or connivent; all alike; dorsifixed, or basifixed; versatile, or non-versatile; dehiscing via pores, or dehiscing via longitudinal slits; latrorse, or 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 straight, or curved, or hooked, or bent. Style terete (thick). Style glabrous. Stigmatic tissue terminal, or oblique. Carpel 4–25 ovuled (to ‘many’, rarely 1). Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile to stipitate. Ovules pendulous to ascending; biseriate; non-arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit stipitate to sessile; non-fleshy; spinose (commonly), or not spinose (smooth, spiny or tuberculate). The fruiting carpel dehiscent to indehiscent (‘more or less’ or ‘scarcely dehiscent’); a legume, or a loment. Pods globose to much elongated (much exserted from the calyx); not triangular; usually coiled (with 1–7 coils); not becoming inflated. Fruit 1 celled. Dispersal unit the seed, or the fruit. Fruit 3–15 seeded (usually one or two in each coil). Seeds endospermic, or non-endospermic; not mucous; small; non-arillate. Cotyledons 2; accumbent. Embryo chlorophyllous; (in-) curved, or bent (the radicle inflexed?). Testa non-operculate. Micropyle zigzag, or not zigzag. Seedling. Germination phanerocotylar.

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

Geography, cytology, number of species. Adventive. 2n=(14, 16, 32, (48). A genus of about 50 species; 13 species in Western Australia.