Croton macrostachyus is a deciduous tree 3-25 m high, although more commonly 6-12 m; crown rounded and open with large spreading branches. Bark pale gray or gray-brown, finely reticulate, fairly smooth, finely fissured with age; slash reddish; shoots densely and shortly hairy. Leaves large, green, turning to orange before falling, ovate, base subcordate or rounded, apex acuminate, margin crenulate-serrulate or subentire, 5-19 x 3.5-15 cm, stellate hairy but more densely so beneath on long stems crowded at the ends of branchlets; veins prominent with 2 stalked glands just visible at the base of the leaf, paler below due to soft hairs; texture more or less furry, margin slightly toothed. Flowers creamy to yellow-white, sweetly scented, to 3 mm long, dioecious or at least on separate shoots, in erect spikes, all over the tree, sometimes a few females accompanying the males, appearing only briefly with the flower spike turning down as fruits mature. Male inflorescence up to 25 cm long, flowers pedicellate. Female inflorescence usually less than 10 cm long and subsessile. Fruits green when young, turning grey at maturity, on drooping spikes to 30 cm long, 3-lobed, 8-9 x 8-10 mm, stellate-pubescent covered at 1 end by a soft, creamy envelope. Fruits mature when still on the tree, splitting open with a sharp noise to release seeds. Each pea-sized capsule contains 3 shiny grey seeds with a soft, cream aril. The generic name is derived from the appearance of the seed, for ‘croton’ is based on the Greek word for a tick. The specific epithet is from the Greek macro- (large) and –stachyus (relating to a spike) hence “with a large spike”.