Melilotus Mill.

Scientific Description

Family Papilionaceae. Trifolieae.

Habit and leaf form. Herbs; not resinous. Annual, or biennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Helophytic, or mesophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; not imbricate; petiolate; non-sheathing; not gland-dotted; 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; 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; via hymenoptera (mainly by bees).

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes (slender). Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences axillary. Flowers pedicellate; bracteate (minute), or ebracteate; ebracteolate; small to medium-sized; 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; more or less 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, or not appendiculate. 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; not laterally spurred. Standard ‘normally’ developed (obovate or oblong). Keel conspicuously exceeded by the wings (usually), or about equalling the wings; not long-acuminate/beaked (blunt); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); white, or yellow; deciduous. Petals clawed, or sessile. 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 or all of them with filaments basally united to form an adaxially split tube); 2 - adelphous (1+9, the vexillary member free of the tube), or 1 - adelphous (the vexillary sometimes connate with the rest); 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. 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 (in-) curved (above). Style filiform. Style glabrous. Stigmatic tissue terminal. Carpel 1–5 ovuled (‘few’). 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 aerial; non-fleshy; not spinose. The fruiting carpel indehiscent; nucular. Pods globose, or somewhat elongated (subglobose or ovoid, as long as the calyx); not triangular; straight; not transversely septate. Fruit 1 celled. Dispersal unit the seed, or the fruit. Fruit 1–3 seeded. 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=16 (32). A genus of about 20 species; 4 species in Western Australia.