Leptosema Benth.

Scientific Description

Family Papilionaceae. Mirbelieae.

Sometimes included in Leguminosae.

Habit and leaf form. Shrubs (or undershrubs). Switch-plants; with the principal photosynthesizing function transferred to stems (the stems sometimes winged). Leaves much reduced (to scales). Plants spiny, or unarmed. The spines when present, axial. Leaves (scales) cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.3–1 m high. Self supporting, or climbing; sometimes scrambling (or trailing). Xerophytic. Cladodes unarmed, or spine-tipped, or modified into spines. Leaves alternate, or opposite, or whorled; when alternate, spiral; not decurrent on the stems; with blades, or bladeless; membranous; non-sheathing; simple; epulvinate. Leaf blades flat; cross-venulate. Leaves without stipules. Leaf anatomy. Complex hairs present, or absent (? — peltate hairs absent). Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the disk. Ornithophilous.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; crowded at the stem bases, or not crowded at the stem bases; terminal, or axillary (or in notches on the winged stems). Inflorescences simple, or compound; terminal, or axillary (or crowded on short, radical scapes). Flowers pedicellate to subsessile; bracteate; bracteolate; small to medium-sized; very irregular; zygomorphic. The floral asymmetry involving the perianth and involving the androecium. Flowers papilionaceous; 5 merous; pentacyclic. Free hypanthium present, or absent. Hypogynous disk absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; five lobed (not ribbed); toothed. Calyx lobes markedly shorter than the tube to markedly longer than the tube. Calyx erect; valvate; exceeded by the corolla; bilabiate (the lobes more or less equal, the posterior pair more or less connate); persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate, or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the keel members ‘dorsally connate’). The joined petals anterior. The wings of the corolla free from the keel; not laterally spurred. Standard markedly reduced (and narrow, folded or recurved); entire. Keel conspicuously exceeding the wings; not long-acuminate/beaked; neither coiled nor spiralled; not bent and beaked. Corolla imbricate; green, or red (usually), or yellow, or green and yellow, or black (almost). Petals clawed. Androecium present. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal to markedly unequal; free of one another; 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 connivent; all alike; dorsifixed; 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 filiform. Style glabrous. Carpel 4–22 ovuled (‘several’). Placentation marginal. Ovary sessile to stipitate. Ovules arillate.

Fruit and seed features. Fruit stipitate to sessile; non-fleshy. The fruiting carpel dehiscent; a legume. Pods globose to much elongated; not triangular; straight, or curved; not beaked; becoming inflated, or not becoming inflated; somewhat compressed to terete; not constricted between the seeds; wingless. Fruit 1 celled. Seeds not triangular, but lobed; not mucous; non-arillate. Cotyledons 2. Embryo bent (radicle inflexed). Testa non-operculate; homogeneous in colour. Micropyle zigzag, or not zigzag.

Physiology, biochemistry. Photosynthetic pathway: C₃.

Special features. Upper lip of calyx lobed; 2 lobed. Lower lip of calyx lobed; 3 lobed.

Geography, cytology, number of species. Australian. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province. 2n=16(32); ploidy levels recorded 2 and 4. A genus of 8 species; 8 species in Western Australia.

Additional comments. Note that if Crisp (1995: ‘Brachysema has no bracteoles’) is to be believed, the cladistic data of Crisp and Weston (1995, Table 2) incorporate a transposition error re presence of bracteoles in Leptosema and Brachysema.