Common name. Opilia Family.
Habit and leaf form. Trees and shrubs, or lianas. Partially parasitic. On roots of the host. Self supporting, or climbing. Mesophytic. Leaves alternate; non-sheathing; simple. Leaf blades entire (turning a characteristic yellow-green on drying); pinnately veined; cross-venulate. Leaves without stipules. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite, or functionally male, or functionally female. Unisexual flowers present, or absent. Plants hermaphrodite, or dioecious (infrequently).
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes, in panicles, in spikes, and in umbels. Inflorescences axillary, or cauliflorous. Flowers small; fragrant (at least sometimes), or odourless; regular; 4 merous, or 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present; of separate members (alternating with the stamens). Perianth with distinct calyx and corolla, or sepaline (the corolla usually absent in female flowers); 4–5 (female flowers), or 8, or 10; 1 -whorled (female flowers), or 2 -whorled; isomerous. Calyx 4, or 5; 1 -whorled; gamosepalous; lobulate (the lobes sometimes almost obsolete), or blunt-lobed; open in bud; cupuliform; regular; persistent; non-accrescent. Corolla 4, or 5; 1 -whorled; polypetalous, or gamopetalous (sometimes basally connate); valvate; regular. Fertile stamens present, or absent (female flowers). Androecium 4, or 5. Androecial members free of the perianth, or adnate (to the corolla); free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 4, or 5; isomerous with the perianth; nearly always alternisepalous. Anthers dehiscing via longitudinal slits; tetrasporangiate. Fertile gynoecium present, or absent (male flowers). Gynoecium 2–5 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth to isomerous with the perianth. Gynoecium syncarpous; eu-syncarpous; superior to partly inferior (sometimes half immersed in the disk). Ovary unilocular; 1 locular. Gynoecium non-stylate, or stylate. Styles attenuate from the ovary; apical; when present, shorter than the ovary at anthesis. Stigmas 1; sometimes capitate. Placentation basal, or free central. Ovules in the single cavity 1; pendulous (usually), or ascending (rarely, when basal); non-arillate; anatropous.
Fruit and seed features. Fruit fleshy; indehiscent; a drupe; 1 seeded. Seeds endospermic. Endosperm oily. Seeds without a testa. Embryo well differentiated (though rather small). Cotyledons (2–)3, or 4. Testa lacking. Seedling. Germination cryptocotylar.
Geography, cytology, number of species. World distribution: pantropical. X = 10. 28 species.
T.D. Macfarlane, L. Watson, N.G. Marchant