Dioecious shrubs or trees with milky exudate. Leaves deciduous, alternate, imparipinnate, petiolate; leaflets opposite, sessile to very short petiolulate, crenate. Inflorescences terminal; male flowers arranged in pendent or erect panicles, female flowers tightly arranged in 3-flowered clusters subtended by an involucre (2 flowers abort); male flowers pedicellate, females sessile; calyx 3–8-parted in male flowers, 0 in female flowers; corolla 0; androecium haplostemonous; pistillode and staminodes 0; disk 0; carpels 3; styles slightly basally connate, apical; stigmas 3; ovule pendulous, basal. Syncarp samaroid, with little-dilated peduncle with parallel margins, 1-locular; exocarp brown.
A single species, O. huaucui, endemic to western Peru. Together with Amphipterygium, this genus is often segregated into the family Julianiaceae, but morphological and molecular data place it well within Anacardiaceae.
Original Publication: Orthopterygium Hemsl. in Phil. Trans. Roy. Soc. London B, 199: 190 (1907).