Sesbania Scop.

Scientific Description

Family Papilionaceae. Robinieae.

Habit and leaf form. Trees, or shrubs, or herbs. The herbs annual, or biennial, or perennial; plants with neither basal nor terminal concentrations of leaves; to 0.5–12 m high. Helophytic, or mesophytic (generally in habitats permanently wet or subject to waterlogging, the stems usually rooting adventitiously in standing water). Leaves small to large; alternate; spiral; ‘herbaceous’, or leathery; not imbricate; petiolate to subsessile; non-sheathing; gland-dotted, or not gland-dotted; compound; pulvinate; pinnate; paripinnate. Leaflets 14–70. Lateral leaflets alternate to opposite. Leaflets stipellate, or not stipellate; flat, or folded; without lateral lobes. Leaf blades dorsiventral. Leaves with stipules. Stipules intrapetiolar; free of one another; caducous (usually), or persistent. Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Glandular hairs absent; complex hairs absent. Branched hairs absent. Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening developing from a conventional cambial ring. Roots. Aerial roots usually present.

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

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences axillary. Flowers pedicellate; bracteate. Bracts deciduous (caducous). Flowers bracteolate. Bracteoles deciduous (caducous). Bracteoles not adnate to the receptacle. Flowers small to large; 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 developing a gynophore. Free hypanthium present (conspicuous). Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; five lobed (the lobes deltate to subulate); hairy (the lobes shortly woolly inside); imbricate, or valvate; exceeded by the corolla; regular (the lobes more or less equal); persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate (wing and keel petals basally lobed, standard sometimes with auricles), or not appendiculate. Standard appendaged (with lateral calli), or 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, or not laterally spurred. Standard ‘normally’ developed; not sericeous. Keel not long-acuminate/beaked (blunt or obtusely acuminate); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); plain, or with contrasting markings; white, or yellow, or orange, or yellow and red, or yellow and purple (often streaked with red or purple); deciduous. Petals clawed. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal to markedly unequal; coherent (forming an adaxially split tube); 2 - adelphous (9+1, the tenth, posterior stamen free of the rest and characteristically bent at the base with the staminal sheath); 1 -whorled (though diplostemonous). Androecium exclusively of fertile stamens. Stamens 10; diplostemonous; both opposite and alternating with the corolla members. Anthers separate from one another, or connivent; all alike; dorsifixed; 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 curved. Style glabrous, or hairy but not bearded (all round, rarely). Stigmatic tissue terminal. Carpel 5–50 ovuled (‘many’). Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary stipitate. Ovary summit glabrous. Stigmas capitate. Ovules pendulous to ascending; biseriate; arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit (50–)70–700 mm long; stipitate; non-fleshy; not hairy; not spinose. The fruiting carpel dehiscent; a legume. Pods much elongated; not triangular; straight, or curved; beaked; not becoming inflated; somewhat compressed, or terete; regularly constricted between adjacent seeds, or irregularly constricted, or not constricted between the seeds; transversely septate between the seeds; winged (rarely), or wingless; when winged, 4. Fruit 1 celled. Dispersal unit the seed. Fruit 5–50 seeded. Seeds endospermic, or non-endospermic; not mucous; non-arillate. Cotyledons 2; accumbent. Embryo curved, or bent. 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. Native of Australia. 2n=12. A genus of about 50 species; 6 species in Western Australia.