Dischidia (PROSEA)
Introduction |
Dischidia R.Br.
- Protologue: Prodr.: 461 (1810); Asclepiadeae: 21 (1810).
- Family: Asclepiadaceae
- Chromosome number: x= unknown;D. major: 2n= 22
Origin and geographic distribution
Dischidia comprises about 40 species and occurs in eastern India, Burma (Myanmar), Indo-China, southern China, Thailand, throughout the Malesian region, and north-eastern Australia. Peninsular Malaysia is richest in species (23), followed by Borneo (about 13), and Sumatra and the Philippines (each about 11).
Uses
Dischidia is commonly used in traditional medicine in South-East Asia; mostly the latex and leaves in external applications, e.g. to treat ringworm, eczema, herpes, burns, wounds and goitre. Decoctions of leaves and whole plants are used internally against gonorrhoea, framboesia (yaws), liver dysfunction and peptic ulcers, and as an anti-inflammatory, and a decoction of the roots is used to cure cough.
Whole plants of D. chinensis Champ. ex Benth. are used in Vietnam to treat cough, pimples, wounds and snake bites. In Vietnam, a decoction of whole D. acuminata Costantin plants is taken as a diuretic in cases of urethritis. Whole plants of this species, mixed with Hoya kerrii Craib, are used in Thailand to treat enlarged liver and cirrhosis, whereas the leaves are applied against liver dysfunction in a mixture with Coelogyne trinervis Lindley stems and Hoya kerrii leaves. In Taiwan D. formosana Maxim. is used in traditional medicine as an anti-inflammatory and diuretic. Dischidia is occasionally cultivated as an ornamental.
Properties
A 50% hydro-ethanolic extract of dried whole plants of D. bengalensis showed no antitumour activity against Leuk-P388 cell lines in mice in vivo.
A steroid, disformone, and a triterpenoid, dischidiol, together with salicylic acid, friedelin, friedelinol, β-amyrin acetate, glutinone, taraxerol, kaempferol, quercetin, isorhamnetin and sitosteryl-3-O-β-glucopyranoside, were isolated from whole D. formosana plants from Taiwan.
Botany
Epiphytic succulent herbs, with slender, twining stems up to 4 mm in diameter, and nodal roots, with or without adventitious roots; white latex present. Leaves opposite, rarely also alternate leaves on same plant, simple, usually ovate or elliptical in outline and flat or lens-shaped in cross-section, but sometimes with shell-like leaves convex in cross-section, or with pitcher leaves in tight clusters together with flat, ovate leaves on elongate stems, or with oblanceolate leaves flat to round in cross-section, entire, usually glabrous, usually with extrafloral nectary at base of lamina, petiolate or not; stipules absent. Inflorescence an axillary or terminal, often umbelliform raceme, up to 10-flowered. Flowers bisexual, regular, 5-merous; calyx small, often with a gland in the angles of the lobes; corolla urceolate, fleshy, sometimes corolline corona present as small lobes alternating with the corolla lobes or as an annulus in the corolla throat, staminal corona composed of hyaline appendages with 2 incurved or reflexed lobes often present, with nectary at base of each appendage; stamens inserted at base of corolla tube, shortly connate at base, with solitary pollinium in each anther cell; ovaries 2, free, superior, 1-celled, stigma conical, enclosed by stamens. Fruit consisting of 1-2 follicles, terete, reniform or semi-terete in cross-section, usually acuminate at apex, usually pendent, many-seeded. Seeds ovate, flat, comose.
The flowers are probably pollinated by insects with a long proboscis, such as moths. Ants often inhabit leaf cavities, but probably do not play a role in pollination. Fruits are rarely produced. Germination is rapid, and there is no apparent resting period.
Ecology
Dischidia comprises both lowland and mountain species. It usually climbs on the trunk and branches of trees, often in sunny or slightly shaded localities, and attaches by its roots. The leaves are often closely appressed, providing a dark and humid environment for the roots. In some species (e.g. D. major ) the roots grow into the cavity of pitcher-like leaves, which are often inhabited by ants. Nitrogen is derived from debris deposited into the leaf cavities by the ants, whereas the inner surface of the cavities has numerous stomata, through which the plant utilizes the carbon dioxide respired by the ants.
Management Brick fragments or wood crumbs, with the addition of nutrients from commercial fertilizer in the recommended amount for epiphytic orchids, are optimum substrates for establishing Dischidia seedlings. When moistened, seeds of D. nummularia , showed 100% germination in this medium.
Genetic resources
The Dischidia species treated here (except D. purpurea ) are widely distributed and locally common, and consequently not in danger of genetic erosion. However, several other species are endemic to comparatively small regions (e.g. 8 species are only found in Peninsular Malaysia) and may easily become endangered. Some destruction of local populations is reported from Australia due to popularity in horticulture.
Prospects
For plants with such a widespread application in traditional medicine, surprisingly little research has been done on the phytochemistry and pharmacological properties of Dischidia . They may be interesting medicinal plants for controlled use, particularly for external applications, also because they seem easy to cultivate.
Literature
157, 169, 170, 671, 793.
Selection of species
Authors
Wongsatit Chuakul, Noppamas Soonthornchareonnon & Orawan Ruangsomboon