Perennial, glabrous herbs without aerial stem, often tufted from a horizontal or vertical, sympodial rhizome bearing scale-like leaves. Leaves distichous, glabrous, eligulate, base sheathing, petiole well-defined, lamina entire, lanceolate, dorsiventral, enrolled in bud; venation pinnate-parallel with the secondary veins emerging from the prominent main vein at narrowly acute angles and regularly connected by fine transversal veins (conspicuous in dried material, but not in living plants). Inflorescence dense or lax, consisting of irregularly branching monochasial cymes. Flowers bracteate, bisexual, epigynous, with the ovary prolonged into a solid extension. Sepals (outer tepals) 3, sub-equal, narrow, fused basally into a tube. Petals (inner tepals) 3, very unequal, the two lateral small, narrow, the median large, forming a variously shaped labellum. Stamens 5, free from each other, the upper median reduced; filaments short, adnate to the base of the petals; anthers tetrasporangiate, introrse, opening by long slits, apically terminated by a short connective tip. Ovules numerous, anatropous, bitegmic, crassi-nucellate. Fruit a dry, loculicidal, elongate capsule terminated by a beak formed by the proximal part of the ovary extension. Seeds numerous, globose, hairy, endospermous, with a lacerate aril and an operculum opposite the radicle.
from southern tropical China (Kwang- tung and Hainan), through Vietnam, Laos, and Thailand, in Malesia to West Malaysia and Borneo: present
The ten species are distributed from southern tropical China (Kwang- tung and Hainan), through Vietnam (1), Laos (1), and Thailand (1), in Malesia to West Malaysia and Borneo. It has frequently been reported in recent literature from 'Pacific islands'. This is probably due to an error.from southern tropical China (Kwang- tung and Hainan), through Vietnam, Laos, and Thailand, in Malesia to West Malaysia and Borneo
The genus has no economic importance and is not often cultivated; O. maxillarioides is, however, often grown as a greenhouse plant. Many species are known only from a few collections, or even from the type collection alone. The author has studied several populations of O. siamensis in nature in southern Peninsular Thailand. Future research should concentrate on inflorescence structure, pollination and dispersal biology.
H.J.P. Winkl. - in Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 15a. 1930: 541
K. Schum. - in Engl. & Prantl, Nat. Pflanzenfam. Nachtr. 1. 1897: 90.
Ridley - in J. Str. Br. Roy. As. Soc. 1899
K. Larsen - in Bot. Tidsskr. 1961: 348
K. Larsen - in Nordic J. Bot. 1993: 285
Ridley - in Fl. Malay Penins. 1924: 291
Baker - in Hook.f., Fl. Brit. India 6. 1892: 263
Holttum - in Gard. Bull. Sing. 1970: 239
K. Larsen - in Fl. Thailand. 1972: f. 10
K. Larsen - in Fl. Camb., Laos & Vietnam. 1983: 147
Nakai - in J. Jap. Bot. 1941: 189
T.L. Wu & S.-J. Chen - in Fl. Reip. Pop. Sinica. 1981: 19.
T.L.Wu - in Acta Phytotax. Sin. 1964: 343