Brachystelma R.Br.

Scientific Description

Family Asclepiadaceae.

Sometimes included in Apocynaceae. Subfamily Asclepiadoideae, Tribe Stapelieae. In some species the tubers may be eaten raw or after cooking in hot ashes (Forster, 1996).

Habit and leaf form. Herbs. ‘Normal’ plants. Perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.2–0.85 m high (Australian species); tuberous. Mesophytic. Leaves small, or medium-sized; not fasciculate; opposite; not decurrent on the stems; ‘herbaceous’; not imbricate; usually sessile, or petiolate; with ‘normal’ orientation; simple; epulvinate. Leaf blades dorsiventral; entire; flat; narrowly linear, or ovate; pinnately veined; cross-venulate; attenuate at the base. Mature leaf blades adaxially glabrous, or pubescent (or with scattered hairs); abaxially glabrous, or pubescent (or with scattered hairs). Leaf blade margins entire; flat.

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

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in umbels. Inflorescences simple; axillary; ascending. Flowers pedicellate; small; regular; 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled. Corolla present; 5; 1 -whorled; appendiculate; gamopetalous; lobed; lobulate. Corolla lobes about the same length as the tube, or markedly shorter than the tube (rarely). Corolla valvate; rotate, or campanulate, or funnel-shaped, or tubular; regular; darkly hairy adaxially (purple in B. glabrifolium), or glabrous adaxially; variously coloured. Corolla lobes ovate, or oblong. Androecium present. Androecial members definite in number. Androecium 5. Androecial members adnate (epipetalous); united with the gynoecium (as a gynostegium); all equal; coherent (connate); 1 -whorled. Stamens 5; all more or less similar in shape (not markedly capitate); isomerous with the perianth. Filaments appendiculate (in both staminal and interstaminal gynostegial coronas); connate into a tube, adnate to stigma. Anthers all alike; appendaged. The anther appendages apical. Pollen shed in aggregates; in tetrads. Gynoecium 2 carpelled. The pistil 2 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylous; superior. Ovary plurilocular; 2 locular. Gynoecium stylate. Styles 2; partially joined (at the stylehead); apical. Stigmas 1; depressed-globose. Placentation axile. Ovules 30–50 per locule (‘many’).

Fruit and seed features. Fruit 6–12 mm long; dehiscent; 1 locular (in 2 follicles, with one often aborting). Dispersal unit the seed. Seeds endospermic; compressed (ovate); conspicuously hairy (comose at micropylar end); with a tuft of hairs. Cotyledons 2.

Geography, cytology, number of species. World distribution: mainly centred in southern Africa. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. 1 native species in northern tropical Australia. A genus of 100 species; 1 species in Western Australia; B. glabriflorum (F.Muell.) Schltr.; 0 endemic to Western Australia.

Additional comments. From the Greek brachy (short) and stelma (crown), alluding to the short staminal corona of some species.

Additional characters Calyx with colleters (secreting mucilage) (at sinus bases). Annular corona absent. Corolline corona absent. Gynostegial corona present; consisting of lobes (incumbent of backs of anthers); staminal, or interstaminal. Gynostegial staminal corona without a conspicuous hump; without an adaxial appendage. Corpusculum ovate. Caudicles winged; not geniculate. Pollinia in the anther locule erect, or horizontal; pellucid germinating mouth of pollinia present; pellucid germinating mouth of pollinia located on inner margin. Pollen tetrads linear. Mature leaf blades bearing colleters (at lamina base), or lacking colleters (usually).

Etymology. From the Greek for "short" and "crown", alluding to the short staminal corona of some species.