Habit and leaf form. Trees, or shrubs; deciduous, or evergreen. ‘Normal’ plants. Leaves well developed. Plants with roots; non-succulent; spiny; autotrophic. To 12 m high (in Australia). Self supporting. Not heterophyllous. Leaves medium-sized; not fasciculate; alternate; with blades; petiolate, or subsessile; with ‘normal’ orientation; simple; not peltate. Leaf blades entire; ovate; 3 -nerved; palmately veined; oblique at the base (‘distinctly asymmetric’). Mature leaf blades adaxially glabrous; abaxially sparsely to moderately pubescent. Leaves with stipules. Stipules spiny; caducous (in WA). Leaf blade margins ‘distantly and shallowly’ crenate (in WA, Z. quadrilocularis). Leaf anatomy. Hairs present, or absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes, or in umbels. Inflorescences compound. The terminal inflorescence unit cymose. Inflorescences axillary. Flowers pedicellate; minute; regular; 5 merous; cyclic; tetracyclic, or tricyclic. Free hypanthium present. Perianth with distinct calyx and corolla (in WA); 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed; glabrous, or hairy; valvate; regular. Calyx lobes triangular. Epicalyx absent. Corolla present (in WA); 5; 1 -whorled; alternating with the calyx; polypetalous; regular; green and yellow. Petals spathulate; hooded. Androecium present. Fertile stamens present. Androecial members definite in number. Androecium 5. Androecial members adnate (to the base of the sepals); free of the gynoecium; free of one another; 1 -whorled. Stamens 5; all more or less similar in shape; isomerous with the perianth; alternisepalous; filantherous. Anthers separate from one another; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Fertile gynoecium present. Gynoecium (3–)4 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synovarious, or synstylovarious, or eu-syncarpous; inferior (and immersed in the disc). Ovary plurilocular; (3–)4 locular. Gynoecium stylate. Styles 1; apical. Stigmas (3–)4 - lobed. Ovules 1 per locule (in WA); ascending; anatropous.
Fruit and seed features. Fruit aerial; 10–18 mm long (in WA); indehiscent; a drupe. Dispersal unit the seed, or the fruit (rarely). Seeds 1 per locule.
Geography, cytology, number of species. Native of Australia, or adventive. Endemic to Australia, or not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province. A genus of ca 100 species; 1 species in Western Australia; Z. quadrilocularis F.Muell.; 0 endemic to Western Australia.
Etymology. Name used by Pliny for Z. vulgaris, from the Arabic zizouf, the name of a species of the genus.