14. Rhomboda Lindley, J. Proc. Linn. Soc., Bot. 1: 181. 1857.
菱兰属 ling lan shu
Authors: Xinqi Chen, Stephan W. Gale, Phillip J. Cribb & Paul Ormerod
Herbs, terrestrial or rarely epiphytic. Rhizome creeping, several noded, fleshy; roots fibrous, villous, arising from rhizome nodes. Stem erect, glabrous, with a few tubular sheaths at base, leafy. Leaves usually crowded at stem apex, green-red, midvein often white, lanceolate, ovate, or elliptic, oblique, apex acute, with a petiole-like base dilating into tubular amplexicaul sheath. Inflorescence erect, terminal, racemose, pubescent; peduncle with a few scattered sheathing bracts; rachis laxly to subdensely few to many flowered; floral bracts sparsely pubescent. Flowers not opening widely, obliquely resupinate or not resupinate; ovary and pedicel not twisted, glabrous to sparsely pubescent. Sepals free, similar, ovate-elliptic, outer surface glabrous to sparsely pubescent. Petals connivent with dorsal sepal and forming a hood, often broadly dilated, membranous; lip adnate to ventral margin of column, 2-partite or with a short mesochile and 3-partite; hypochile saccate, with a low, longitudinal carina along midvein forming a large, raised bicarinate callus toward apex of hypochile, and with 1 fleshy, undivided callus on either side near base; exterior of hypochile with fleshy flanges; mesochile (when present) short, margin involute; epichile linear, quadrate or transversely dilated, simple or 2-lobed. Column short, abruptly dilated apically, with 2 large, parallel wings; anther ovoid, 2-locular; pollinia 2, clavate, attached to a solitary, small, ovate viscidium; rostellum deltoid, short, broad, remnant shortly bifid; stigma lobes 2, separate, placed laterally at column apex, convex. Capsule erect.
About 25 species: from the Himalayas and NE India, across S and SE China to S Japan, and throughout SE Asia to New Guinea and the SW Pacific islands; four species (one endemic) in China.
The genus Rhomboda was recently reinstated by Ormerod (Orchadian 11: 323-339. 1995), having been neglected (with its constituent taxa being variously referred to Hetaeria, Zeuxine, or Odontochilus) for over a century. Species belonging to Rhomboda can be distinguished by the medial bicarinate callus within the hypochile of the lip (in addition to the two large, often stalked, basal calli) in combination with the flanges on the exterior surfaces of the hypochile and the presence of two large wings on the column. Most of the Chinese species remain poorly known.