Epiphytes or lithophytes with creeping branched rhizomes anchored by filamentous roots and short, single-noded pseudobulbs crowded to widely spaced and erect on the rhizomes. Each pseudobulb has a single large terminal leaf that is longer than wide, flat, thick and leathery. The flowers are borne terminally on long scapes with the flowers spread out in a semicircular umbel-like pattern at the apex. The flowers, which range from small to relatively large, are often scented. The dorsal sepal is smaller than the lateral sepals and the petals, which are a similar size to the dorsal sepal, are usually hairy. The bases of the lateral sepals are fused to the column foot and then abruptly twisted to form a convex blade with the anterior margins fused and forming a cavity or tunnel around the labellum. The labellum, which is unlobed and fleshy, is hinged to the apex of the column foot and delicately balanced. The flowers last several days.
Significant Generic Characters
Epiphytic/lithophytic orchids; plants appressed; roots filamentous; rhizomes creeping; pseudobulbs single-noded; leaf large, terminal, flat, thick, leathery; inflorescences arising from the base of a pseudobulb, multiflowered, the flowers borne terminally in a semicircular umbel-like pattern; dorsal sepal smaller than the lateral sepals; petals similar to the dorsal sepal, usually hairy; lateral sepal bases fused to the column foot and then abruptly twisted to form a convex blade with the anterior margins connate and forming a cavity or tunnel around the labellum; labellum delicately hinged to the apex of the column foot, unlobed, fleshy.
Size and Distribution
A genus of about 75 species distributed in Asia, South-East Asia, Malaysia, Philippines, Indonesia, New Guinea, Solomon Islands, Polynesia and Australia. Two non-endemic species occur in Queensland. Cirrhopetalum clavigerum Fitzg. is restricted to the McIlwraith Range on Cape York Peninsula and Cirrhopetalum gracillimum Rolfe occurs further north in the Janet and Tozer Ranges near Iron Range. State occurrence: Queensland.
Ecology
Both native species of Cirrhopetalum occur in rainforest at low to moderate altitudes, growing on trees and rocks on slopes and ridges as well as near streams. They are usually found in situations where the humidity is relatively high and there is good air movement. These orchids occur in tropical regions where the majority of the rain falls during the summer wet season (December to March) and the remaining months are much drier, with sporadic or intermittent rain.
Biology
Pollination: The flowers of both native species of Cirrhopetalum last for a few days and are insect-pollinated. Small flies are the most likely vector, these being attracted to the flowers to feed on nectar that gathers on the labellum.
Reproduction: Reproduction in Cirrhopetalum is solely from seed. Seed dispersal of these orchids takes 4-6 months after pollination and the capsules develop in an erect position. There is no increase in the length of the peduncle or pedicel during this process. Apomixis is unknown in the genus.
Seasonal Growth: The plants grow strongly during the summer months and for a period after the wet, and are relatively quiescent for the remainder of the year.
Flowering: Flowering takes place mainly in the spring and summer months.
Hybrids: Natural hybrids involving the native species of Cirrhopetalum are unknown.
Derivation
The generic name Cirrhopetalum is derived from the Latin cirrus, tendril and petalum, petal. It apparently refers to the long lateral sepals that in some species curl inwards towards the apex.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Roots filamentous, produced from along the rhizomes and the bases of pseudobulbs. Rhizomes appressed to the host, well developed, sturdy, creeping, much branched, covered by closely sheathing, imbricate, scarious bracts that break down and leave the fibrous ribs. Pseudobulbs erect, in-line, crowded to widely spaced, single-noded, ovoid, conical or shortly cylindric, fibrous. Trichomes present or absent. Leaves subsessile to shortly petiolate, 1- per shoot, terminal on a pseudobulb, not sheathing at the base, flat, longer than wide, smooth, thick, coriaceous; apex unequally emarginate. Inflorescence arising from the base of a pseudobulb, erect to arcuate, ending in a pseudo-umbel with the flowers spread out in a semi-circular pattern. Peduncle much longer than the pedicels, with 2-3 sheathing or spreading, tubular or flat sterile bracts. Floral bracts free, small, sheathing the base of a pedicel. Pedicel much shorter than the peduncle, spreading, straight, merging with the ovary. Ovary elongate, straight, smooth, merging with the pedicel. Flowers resupinate, pedicellate, facing upwards or outwards, lasting a few days, dull coloured (white, cream, yellowish, red or purplish), with a fruity or musty scent. Perianth segments thin to firm-textured. Dorsal sepal free, smaller and of a different shape to the lateral sepals, hooded, glabrous or hirsute; apex often aristate or setiferous. Lateral sepals much larger than the dorsal sepal, attached by their bases to the column foot then abruptly twisted once so as to form a convex blade with fused anterior margins, leaving a cavity or tunnel around the labellum and column. Petals free, shorter and narrower than the dorsal sepal, hairy or pustulate. Labellum hinged by a short claw to the apex of the column foot, delicately balanced, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina more or less ligulate, unlobed, thick and fleshy, curved; margins entire; apex entire. Callus obscure, consisting of a shallow basal channel. Nectar present. Column lacking free filament and style, short, straight. Column wings present, ventral with linear apical stelidia. Column foot well developed, curved upwards at the apex. Anther terminal, incumbent, 2-celled, deciduous, basifixed, smooth or papillate, erostrate. Pollinarium absent. Pollinia 4 in 2 pairs, crescentic, yellow or orange, hard, waxy. Viscidium absent. Rostellum ventral, transverse. Stigma entire, vertical, concave. Capsules dehiscent, glabrous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
The status of Cirrhopetalum as a genus distinct from Bulbophyllum, which has been questioned by many botanists over the years since 1861, was recently clarified and the genus defined (Garay et al., 1994).
Nomenclature
Cirrhopetalum Lindl., Gen. Sp. Orchid. Pl. 45, 58, May (1830). Type species: Cirrhopetalum thouarsii Lindl., nom. illeg.
Zygoglossum Reinw., Syll. Pl. Rastisb. 2: 4, Jan.-Feb. (1826).
Infrageneric Taxa: A genus of 3sections:-
1. Section Cirrhopetalum. Lateral sepals porrect, twisted once to form a convex blade with connate outer margins to form a tunnel-like structure around the labellum; dorsal sepal and lateral sepals rarely separated spatially by the petals; lateral sepals remaining fused.
2. Section Recurvae. Lateral sepals recurved, arching, twisted once to form a convex blade with connate outer margins to form a tunnel-like structure around the labellum; dorsal sepal and lateral sepals separated spatially by the petals; lateral sepals remaining fused.
3. Section Wallichii. Lateral sepals gradually folded inwards to form a convex blade with connate outer margins to form an open structure around the labellum; lateral sepals often separating into free segments with age.
References
Clements, M.A. and Jones, D.L. (2002). Nomenclatural changes in the Australian and New Zealand Bulbophyllinae and Eriinae (Orchidaceae). Orchadian 13(11): 498-501.
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.
Garay, L.A., Hamer, F. and Siegerist, E.S. (1994). The genus Cirrhopetalum and the genera of the Bulbophyllum alliance. Nordic Journal of Botany 14(6): 609-646.
Seidenfaden, G. (1974). Notes on Cirrhopetalum Lindl., Dansk Bot. Arkiv. 29(1): 1-260.
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.