Trees , deciduous; sap milky. Branches with axillary spines. Terminal buds surrounded by bud scales. Leaves alternate; stipules caducous, free. Leaf blade ovate to lanceolate, not leathery, margins entire, never lobed; venation pinnate. Inflorescences: flowers borne outside receptacle; staminate inflorescences loose short racemes; pistillate inflorescences dense heads. Flowers: staminate and pistillate on different plants. Staminate flowers: calyx 4-lobed; stamens 4, inflexed; filaments filiform; anthers introrse, with short connective. Pistillate flowers: sepals 4, 2 outer sepals wider than inner ones; ovary 1, superior, 1-locular; style unbranched, filiform. Syncarps globose, 8-12 cm or more diam.; each achene completely enclosed by its enlarged, fleshy calyx. Maclura is a monotypic genus endemic to North America.
Dioecious; staminate fls numerous in loose, globose to oblong, peduncled axillary heads, with 4-parted cal and 4 stamens; pistillate fls coherent in dense, globose, axillary heads, the 4-lobed cal closely surrounding the ovary, the style filiform and elongate; fr a hard, globose syncarp, composed of the enlarged common receptacle and calyces, completely concealing the achenes; trees, usually thorny, with alternate, entire lvs. 11, mainly warm reg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.