Shrubs or perennial herbs, erect, branched. Stems 4-sided or terete, winged or not on angles, pubescent. Leaves petiolate; leaf blade stiffly papery to papery, secondary veins 2 or 3 on each side of midvein, tertiary veins parallel, margin entire or denticulate. Inflorescences terminal, narrowly panicled cymose, more than 25 × 3-4 cm; bracts often caducous. Pedicel very short. Hypanthium narrowly funnelform or funnelform-campanulate, 4-sided, 8-ribbed but 4 ribs inconspicuous, usually contracted at middle. Calyx lobes very short or inconspicuous. Petals broadly ovate or ovate, apically oblique, apex acute. Stamens twice as many as perianth, subequal in length, inclined to one side; anthers as long as filaments or longer, subulate or oblong-linear, not appendaged at base; connective slightly inflated, not spurred or shortly spurred. Ovary inferior, ovoid or ovoid-globular, 4- or 5-celled, apex 8-10-setose or -denticulate. Style filiform, exserted beyond stamens. Capsule ellipsoid, ovoid, or subglobular; hypanthium longitudinally 8-ribbed. Seeds numerous, very small, cuneate, angled, puberulous.

The number of species in Allomorphia is unclear because most species have also been treated in Oxyspora, including the type species, A. exigua (Jack) Blume, and the circumscription of these two genera is currently unresolved.

Allomorphia eupteroton Guillaumin var. teretipetiolata C. Y. Wu & C. Chen (Fl. Yunnan. 2: 93. 1979), described from Yunnan (Jinping), represents a separate species and belongs to Oxyspora according to Shui Yumin (pers. comm. to Renner, 2007). A paper discussing the relationships between this and related taxa, and making the new combination at species rank in Oxyspora, will be published in the near future (Acta Phytotax. Sin. 45. 2007).

Number of species unclear: S China, India, Indonesia, Malaysia; four species (one endemic) in China.