Stylosanthes Sw.

Scientific Description

Family Papilionaceae. Aeschynomeneae.

Habit and leaf form. (Sub-) shrubs, or herbs; resinous, or not resinous. Perennial; plants with neither basal nor terminal concentrations of leaves; to 0.2–1.5 m high. Mesophytic, or xerophytic. Leaves small to large; alternate; spiral; ‘herbaceous’, or leathery; not imbricate; petiolate. Petioles wingless. Leaves compound; pulvinate; ternate. Leaves pinnately trifoliolate. Leaves imparipinnate. Leaflets 3; not stipellate; pulvinate, or epulvinate; flat, or folded; without lateral lobes. Leaf blades dorsiventral. Leaves with stipules. Stipules intrapetiolar. Stipules more or less peltate, or not peltate. Stipules adnate to the petiole (to its lower part); concrescent (sheathing the stem, the leaf born in their sinus); persistent. Leaf blade margins entire. Leaves without a persistent basal meristem. 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 spikes, or in heads (these sessile). Inflorescences compound (contracted, with primary bract, secondary bracts and sometimes plumed axis rudiments); terminal, or axillary. Flowers subsessile, or sessile; bracteate (1–3 foliolate and stipule-like primary, and 2– or 3–lobed secondary); (1 or 2) bracteolate (the bracteoles translucent); small to medium-sized; 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’); basically 5 merous. Floral receptacle with neither androphore nor gynophore. Free hypanthium present (longer than broad). Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; partially gamosepalous, or gamosepalous (the four upper lobes connate for about half their length, the anterior one free); (five) lobed (membranous); imbricate, or valvate; exceeding the corolla; bilabiate; persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate (the wings and keel auriculate and spurred). Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the two ventral petals connivent to form the ‘keel’). The joined petals of the papilionate corolla anterior. The wings of the corolla free from the keel (oblong); laterally spurred. Standard ‘normally’ developed; emarginate; not sericeous. Keel conspicuously exceeded by the wings to conspicuously exceeding the wings; long-acuminate and beaked (and incurved); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); plain, or with contrasting markings; yellow, or yellow and red, or brown; deciduous. Petals shortly clawed. 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; 1 - adelphous (the tube initially closed but splitting later, persistent after the upper parts of the filaments are shed). The staminal tube free from the keel petals. Androecial members 1 -whorled. 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; dimorphic (alternately longer and sub-basifixed, shorter and versatile); dorsifixed, or dorsifixed and basifixed; versatile, or versatile and non-versatile; dehiscing via pores, or dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Pollen shed as single grains. 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 curved. Style long and filiform. Style glabrous. Stigmatic tissue terminal. Carpel 2–3 ovuled. Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile. Ovules pendulous to ascending; biseriate; arillate, or non-arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit aerial; 3–7 mm long; sessile; non-fleshy; hairy to not hairy; not spinose. The fruiting carpel indehiscent; a loment (with 1–2 joints). Pods globose to much elongated; not triangular; more or less straight; beaked (style base persistent, forming a hook); not becoming inflated; regularly constricted between adjacent seeds; transversely septate between the seeds; wingless. Loment segments rounded or cuboid. Fruit 1 celled; elastically dehiscent, or passively dehiscent; (1–)2–6 seeded. Seeds ovate to oblong; endospermic, or non-endospermic; not mucous; compressed; small; arillate, or non-arillate (‘usually’). Cotyledons 2; accumbent. Embryo curved, or bent. 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. Adventive. 2n=20. A genus of about 25 species; 5 species in Western Australia (naturalized, several cultivated for fodder).