Habit and leaf form. Trees, or shrubs (Australian species all erect shrubs or undershrubs); evergreen (usually), or deciduous; laticiferous, or non-laticiferous and without coloured juice; resinous, or not resinous. Partially parasitic. On roots of the host. Leaves cauline. Stem internodes solid. Mesophytic, or xerophytic. Leaves alternate; leathery; petiolate; non-sheathing; gland-dotted, or not gland-dotted; foetid (often malodorous); simple. Leaf blades entire; one-veined (midrib evident, lateral ribs obscure); cross-venulate. Leaves without stipules. Leaf blade margins entire. Leaf anatomy. Hairs absent. Extra-floral nectaries absent. 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. Female flowers with staminodes (small). Male flowers with pistillodes.
Inflorescence and flower features. Flowers solitary (in Australian species), or aggregated in ‘inflorescences’; in racemes, or in spikes (not Australian species). Inflorescences axillary. Flowers pedicellate (short); ebracteate; ebracteolate; small; regular (except sometimes the stamens); cyclic. Free hypanthium present; adnate to the ovary. Hypogynous disk present; annular. Perianth with distinct calyx and corolla; 6–12; 2 -whorled; isomerous. Calyx present; 3–6; 1 -whorled; gamosepalous; entire, or lobed; when not enite, blunt-lobed; imbricate, or open in bud; cupuliform; regular; fleshy, or non-fleshy; persistent; accrescent, or non-accrescent. Corolla present; 5–6; 1 -whorled; alternating with the calyx; polypetalous, or gamopetalous (basal half connate but usually easily parted); valvate; regular; white (creamy), or yellow (pale). Corolla members small uncinate thickening inside at the apex. Fertile stamens present, or absent (female flowers). Androecial members definite in number. Androecium 8–12(–18). Androecial members adnate (to the petals); free of one another, or coherent; 1 -whorled. Androecium including staminodes. Staminodes 5 (1 opposite each petal lobe). Stamens 3(–8); reduced in number relative to the adjacent perianth to polystemonous; when as many as C, alternisepalous. Anthers basifixed; versatile, or non-versatile; dehiscing via longitudinal slits; tetrasporangiate. Fertile gynoecium present, or absent (male flowers). Gynoecium 3 carpelled. The pistil 1 celled, or 3 celled. Carpels isomerous with the perianth, or reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious, or eu-syncarpous; partly inferior (partly immersed in the hypanthium). Ovary unilocular, or plurilocular; 1 locular, or 3 locular (imperfectly 3, 1 above 3 at the base). Gynoecium stylate. Styles 1; apical. Stigmas 1; 3 - lobed. Placentation when unilocular, free central; when plurilocular, axile. Ovules in the single cavity 3; 1 per locule, or 3 per locule (total of 3); pendulous; anatropous.
Fruit and seed features. Fruit fleshy (succulent exocarp formed by the enlarged hypanthium); indehiscent; a drupe, or a nut (one seeded); 3 celled (at base, 1 above); 1 seeded (almost always). Seeds endospermic. Endosperm oily. Cotyledons 2–6. Embryo straight.
Etymology. From the Latin olax (evil smelling); refers to the unpleasant smell of some Asian species. This seems a more appropriate derivation than that given by Linnaeus: from the Greek olax, the Doric from of aulax (a furrow).