Fan Orchids
Epiphytes or lithophytes with very thin roots and a single fan-shaped growth that increases steadily in size. The main stem is swollen and fleshy and covered closely by overlapping leaf bases. The leaves are arranged in 2 ranks with an abscission zone between the blade and the sheathing base. Long thin arching spikes extend through a leaf base and emerge from the base of a blade. They have numerous tiny white cup-shaped flowers. Thin bracts persist on the scape after the flowers fall. Labellum tiny, stiffly attached to the apex of the column foot. Column tiny, with a column foot.
Similar Genera
Significant Generic Characters
Epiphytic/lithophytic monopodial orchids; plants fan-shaped; roots very thin; stems swollen, fleshy, covered with imbricate leaf bases; leaves in 2 ranks; leaf bases laterally flattened, fleshy; lamina articulate on the apex of the leaf base, thinly coriaceous, apex unequally emarginate; racemes axillary, arcuate, growing through a leaf base and emerging from the base of the blade, multiflowered; flowers tiny, lasting 2-4 days, white; sepals and petals relatively broad, porrect to incurved; labellum obscurely 3-lobed, stiffly attached to the apex of the column foot; column short, with a short foot; pollinia 8, in 2 groups of 4, each group forming a separate hemipollinarium.
Size and Distribution
A genus of about 8 species occurring in Indonesia, New Caledonia, Polynesia and New Guinea with a single widespread species, Rhipidorchis micrantha, extending to Australia. The Australian species is distributed between the Iron Range (12°36' S) on Cape York Peninsula, and Tully (17°56' S), in Queensland. State occurrence: Queensland.
Ecology
Rhipidorchis micrantha grows on trees and rocks in lowland rainforest, especially near streams. It favours sheltered humid situations with free air movement. The prevailing climate has a summer wet season (December to March) when the vast majority of rain falls, with the remaining months being much drier and having sporadic to intermittent rain.
Biology
Pollination: The flowers of Rhipidorchis micrantha are tiny, last 2-3 days and the pollinarium is difficult to remove from the anther. However the flowers do not appear to be self-pollinating since the fruit set is very erratic. They are possibly be pollinated by rain splash.
Reproduction: Reproduction in Rhipidorchis is solely from seed. Seed dispersal takes 1-2 months from pollination and the capsules develop in a porrect position. Seedling recruitment sometimes occurs on the swollen base of large plants. Apomixis is unknown in the genus.
Seasonal Growth: Rhipidorchis plants grow actively in summer and autumn and are relatively quiescent for the remainder of the year.
Flowering: Rhipidorchis micrantha flowers mainly October to February but sporadic inflorescences occur at other times.
Hybrids: Natural hybrids are unknown in these orchids.
Derivation
The name Rhipidorchis is derived from the Greek rhipidos, fan and Orchis another genus of Orchidaceae but also applied generally to orchids.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, monopodial. Plants glabrous, fan-like. Roots filamentous, thin. Stems reduced, condensed, swollen, fleshy. Pseudobulbs absent. Trichomes absent. Leaves lasting several seasons, in 2 ranks; base laterally flattened, sheathing, persistent, elongate, fleshy, the bases closely imbricate; lamina articulate on the apex of the sheathing base, conduplicate at the base then flattened, thin-textured, coriaceous; apex unequally emarginate. Venation unknown. Inflorescence spicate, multiflowered, erect or arcuate, axillary, extending through a leaf sheath and emerging at the base of the lamina. Peduncle much shorter than the rhachis, thin, wiry, with scattered sterile bracts. Rhachis thin, straight. Floral bracts short, narrow, spreading, persisting after anthesis. Pedicels absent. Ovary short, straight, smooth. Flowers resupinate, minute, cupulate, crowded, white, sessile to subsessile, opening sequentially in a spiral. Perianth segments short, relatively broad. Dorsal sepal free, similar to the lateral sepals, porrect to incurved. Lateral sepals fused at the base to the margins of the column foot to form a mentum, similar to the dorsal sepal, porrect to incurved. Petals subsimilar to the sepals, usually smaller. Labellum stiffly attached to the apex of the column foot, markedly dissimilar in size to the sepals and petals, ecalcarate. Labellum lamina obscurely 3-lobed, canaliculate proximally; lateral lobes small, suberect; midlobe broadly rounded, margins entire; apex minutely papillate. Spur absent. Callus obscure. Nectar present. Column very short, lacking free filament and style. Column foot relatively long, at a sharp angle to the column. Pseudospur absent. Column wings obscure. Anther terminal, incumbent, 2-celled, persistent, basifixed. Pollinaria 2 (hemipollinaria). Pollinia 8 in 2 groups of 4, clavate, orange, stalked. Viscidium small. Rostellum ventral, broad. Stigma entire, deeply concave. Capsules dehiscent, small, glabrous, porrect; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Rhipidorchis was previously included in Rhynchophreatia (Hallé 1977) but the flowers lack the long rostellum and fleshy backward-projecting callus of that genus. They have also been included in Phreatia from which they can be distinguished by monopodial growth habit, leaves arranged in 2 ranks, the presence of an abscission zone between the sheathing leaf base and the lamina and the presence of a column foot (Jones and Clements 2004).
Nomenclature
Rhipidorchis D.L.Jones and M.A.Clem., Orchadian 14:8: Scientific Supplement xiv-xv (2004).
Type species: Rhipidorchis micrantha (A.Rich.) D.L.Jones and M.A.Clem. [Oberonia micrantha A.Rich.].
Infrageneric Taxa: No infrageneric treatment of Rhipidorchis is available.
References
Dockrill, A.W. (1969). Australian Indigenous Orchids. Volume 1. The Society for Growing Australian Plants, Halstead Press, Sydney.
Dockrill, A.W. (1992). Australian Indigenous Orchids. Volume 1 & 2. Surrey Beatty & Sons in association with The Society for Growing Australian Plants, Chipping Norton, NSW.
Hallé, N. (1977). Flore de la Nouvelle Calédonie et Dependances 8: Ochidacées. Museum National D’Histoire Naturelle, Paris.
Jones, D.L. and Clements, M.A. (2004). Miscellaneous new species, new genera, reinstated genera and new combinations in Australian Orchidaceae. Orchadian 14(8): Scientific Supplement xiv-xv.
Schlechter, R. (1982). The Orchidaceae of German New Guinea (English translation by R.S. Rogers, H.J. Katz and J.T. Simmons). Australian Orchid Foundation, Melbourne.