Marsdenia R.Br.

Scientific Description

Family Asclepiadaceae.

Sometimes included in Apocynaceae. Subfamily Asclepiadoideae, Tribe Marsdenieae. Marsdenia is broadly circumscribed in the current account; as characters previously used to distinguish segregates such as Gymnema and Thozetia have been found unreliable when large numbers of taxa are examined (Forster, 1996).

Habit and leaf form. Shrubs, or lianas, or herbs; laticiferous (with clear, brown, green or white latex). ‘Normal’ plants. Plants with roots (fibrous, fleshy-fusiform or tuberous). Leaves cauline. Self supporting, or climbing. Mesophytic. Leaves medium-sized; not fasciculate; opposite; not decurrent on the stems; not imbricate; petiolate. Petioles wingless. Leaves with ‘normal’ orientation; simple; epulvinate. Leaf blades dorsiventral; entire; flat; ovate, or obovate, or oblong, or elliptic; pinnately veined (or obscure); cross-venulate, or without cross-venules; cordate, or cuneate at the base, or rounded at the base (or truncate). Mature leaf blades adaxially glabrous, or pubescent; abaxially glabrous, or pubescent. Leaf blade margins entire; flat. Leaf anatomy. Hairs present, or absent.

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 racemes (or in 1-many fascicles). Inflorescences simple; axillary. Flowers pedicellate; small, or medium-sized; 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; appendiculate; gamopetalous; lobed; lobulate. Corolla lobes markedly longer than the tube. Corolla imbricate, or valvate; rotate, or campanulate, or urceolate (or salverform); regular; variously coloured. 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 entire or divided lobes adnate to staminal column), or not appendiculate; 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; depressed-globose, conical-elongate to elongate-rostrate. Placentation axile. Ovules 30–50 per locule (‘many’).

Fruit and seed features. Fruit 25–200 mm long; dehiscent; 1 locular (in 2 follicles, with one often aborting). Dispersal unit the seed. Seeds endospermic; compressed (ovate to oblong); conspicuously hairy (comose at micropylar end only); with a tuft of hairs. Cotyledons 2.

Geography, cytology, number of species. Native of Australia, or adventive. Endemic to Australia, or not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, and Australian Capital Territory. Northern Botanical Province. A genus of 250 species; 10 species in Western Australia; 1 endemic to Western Australia.

Additional comments. Named for William Marsden (1754–1836), Irish born orientalist and numismatist, Secretary to the Admiralty, collector of plants in Sumatra.

Additional characters Calyx with colleters (secreting mucilage) (at sinus bases). Annular corona absent. Corolline corona present (and staminal, and comprising 5 ridges of pubescent tissue alternate with corolla lobes), or absent; free from gynostegium (when present). Gynostegium not markedly capitate. Gynostegial corona present (and staminal, and comprising 5 entire or divided lobes adnate to staminal column), or absent; 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 erect; pellucid germinating mouth of pollinia absent. Pollen tetrads linear. Mature leaf blades bearing colleters (at lamina base), or lacking colleters.

Etymology. After William Marsden (1754–1836), secretary of the British Admiralty; orientalist and numismatist, collected in Sumatra and Bencoolen (1771–79) and wrote a history of Sumatra.