Gomphocarpus R.Br.

Scientific Description

Common name. Cottonbushes. Family Asclepiadaceae.

Sometimes included in Apocynaceae. Subfamily Asclepiadoideae, Tribe Asclepiadeae.

Habit and leaf form. Shrubs, or herbs; laticiferous (with white latex). ‘Normal’ plants. Plants with roots (fibrous). Annual, or biennial, or perennial. Leaves cauline. To 2 m high. Mesophytic. Leaves medium-sized; not fasciculate; opposite; not decurrent on the stems; not imbricate; petiolate, or sessile. Petioles wingless (when present). Leaves with ‘normal’ orientation; simple; epulvinate. Leaf blades dorsiventral; entire; flat; elliptic, or oblong; 8–14 -nerved; pinnately veined; cross-venulate; cuneate at the base. 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 (or in 1 or 2 ‘fascicles’(G. cancellatus)). 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; gamosepalous; lobed. Corolla present; 5; 1 -whorled; not appendiculate; gamopetalous; lobed; lobulate. Corolla lobes markedly longer than the tube. Corolla valvate, or imbricate; rotate; regular; pink (in G. cancellatus), or cream, or green and cream. Corolla lobes ovate. Corolla members entire. 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 a staminal gynostegial corona composed of 5 staminal lobes or highly fused staminal and interstaminal parts); connate into a tube, adnate to stigma. Anthers all alike. 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; conical-globose. Placentation axile. Ovules 30–50 per locule (‘many’).

Fruit and seed features. Fruit 40–75 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: occurring in Africa. Adventive. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, and Victoria. South-West Botanical Province. 2 species naturalised in Australia. A genus of 50 species; 2 species in Western Australia; G. fruticosus (L.) W.T.Aiton, G. physocarpus E.Mey.; 0 endemic to Western Australia.

Additional comments. From the Greek gomphos (a nail, peg or bolt) and carpos (fruit), alluding to the shape of the follicles.

Additional characters Calyx with colleters (secreting mucilage) (at sinus bases). Annular corona absent. Corolline corona absent. Gynostegial corona present; consisting of lobes; staminal. Gynostegial staminal corona without a conspicuous hump; without an adaxial appendage. Corpusculum oblong. Caudicles not winged; not geniculate. Pollinia in the anther locule pendulous. Pollen tetrads linear. Mature leaf blades bearing colleters (at lamina base), or lacking colleters (in all naturalised Australian species).

Etymology. From the Greek for "club" and "fruit".