Rope Orchids
Epiphytes or lithophytes. Rhizomes thin, erect to pendulous or appressed, sparsely branched to freely branched, anchored by filamentous roots arising from basal stem nodes and also with some aerial roots that often grow along the rhizomes, or if appressed to the host then roots arising from most stem nodes. Pseudobulbs small, single-noded, well-spaced. Leaf single, small to large, terminal, usually longer than wide, flat or grooved, thick-textured or fleshy. Flowers borne singly at sporadic intervals from a multi-flowered inflorescence that arises from the base of a pseudobulb, upside-down, small and fleshy, lasting a few days, porrect, with no noticeable scent. Petals much smaller than the sepals. Labellum firmly hinged to the apex of the column foot. Labellum lamina obscurely 3-lobed, fleshy, glabrous or hairy.
Similar Genera
Significant Generic Characters
Epiphytic/lithophytic orchids; plants erect, pendulous or appressed; rhizomes thin; roots filamentous, arising from stem nodes; pseudobulbs small, single-noded, well-spaced; leaf single, terminal, flat or grooved, thick-textured to fleshy; flowers borne singly at sporadic intervals from a multiflowered inflorescence that arises from the base of a pseudobulb; flowers non-resupinate, small, fleshy, lasting a few days; petals much smaller than the sepals; labellum firmly hinged to the apex of the column foot; labellum lamina obscurely 3-lobed, fleshy, glabrous or hairy.
Size and Distribution
A genus of about 25 species, a significant number occurring in New Guinea, with 8-9 species endemic in Australia. The genus is also distributed in Thailand, Burma, Laos, Vietnam, Malaysia, Philippines, Borneo, Indonesia and Fiji. State occurrence: Queensland, New South Wales.
Ecology
Species of Oxysepala are found in rainforest and humid locations in open forest. They grow on trees or rocks on sheltered slopes and ridges in situations of shade and moderate to bright light, high humidity and free air movement. The majority of native species grow at moderate to high altitudes in the ranges and tablelands, with O. shepherdii extending to lowland areas in temperate New South Wales.
Biology
Pollination: The flowers of Oxysepala species last 3-4 days and are insect-pollinated, the vectors apparently being small flies that feed on nectar produced by the labellum.
Reproduction: Reproduction in Oxysepala is solely from seed. Seed dispersal takes 4-6 months after pollination. There is no increase in the length or thickness of the peduncle or pedicel during this process. Apomixis is unknown in the genus.
Seasonal Growth: The plants grow actively over the summer months and are relatively quiescent for the remainder of the year.
Flowering: Flowering mainly takes place in winter-spring with the flowers often being produced in sporadic bursts.
Hybrids: Natural hybrids involving species of Oxysepala are unknown.
Derivation
The generic name Oxysepala is derived from the Greek oxy, sharp or pointed and sepalum, sepal. Some species have long-acuminate sepals.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous except for trichomes on the labellum of some species. Roots filamentous, wiry, produced from the base of a pseudobulb; distal nodes with aerial roots. Rhizomes attached to the host by roots from the basal nodes, the remainder arcuate to pendulous, thin, creeping, unbranched or sparsely branched from the base, covered by persistent closely sheathing, imbricate, scarious bracts. Pseudobulbs appressed to the rhizome, more or less alternate, crowded, single-noded, small, cylindric, smooth, fleshy, flattened or broadly grooved on the side away from the rhizome, partly obscured by bracts. Trichomes absent or present on the labella of some species. Leaves sessile, 1-per shoot, terminal on a pseudobulb, not sheathing at the base, flat to shallowly channelled or terete with a deep groove, longer than wide, smooth, thick-textured, fleshy, coriaceous; apex unequal, decurved. Inflorescence arising from the base of a mature pseudobulb, multiflowered but each flower arising singly at sporadic intervals, erect. Peduncle longer than the pedicel, thin, with a single tubular, closely sheathing, membranous sterile bract at the base. Floral bract tubular, membranous, sheathing the base of the pedicel. Ovary short, curved at right angles to the pedicel and merging with it, smooth. Flowers resupinate, pedicellate, porrect to semi-nodding, lasting a few days, dull coloured (whitish or pinkish and heavily striped with red or purple), unscented. Perianth segments thin-textured, moderately spreading. Dorsal sepal free, subsimilar to the lateral sepals; apex cymbiform. Lateral sepals subsimilar to the dorsal sepal, attached by their base to the column foot, the protruding basal part on the anterior side fused; apex cymbiform. Petals free, much smaller than the sepals, entire. Labellum hinged by a short claw to the apex of the column foot, firmly attached, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina more or less ligulate, three-lobed, thick and fleshy, curved; lateral lobes basal, suberect; margins entire; underside with short papillose hairs; apex entire. Spur absent. Callus obscure, consisting of a shallow basal channel. Nectar present. Column lacking free filament and style, short, straight. Column wings present, ventral and with elongated apical stelidia. Column foot well developed, curved upwards at the apex and thickened. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, hinged, smooth or papillate, erostrate. Pollinarium absent. Pollinia 4 in 2 pairs, crescentic, orange, hard, waxy. Viscidium absent. Rostellum ventral, transverse. Stigma entire, vertical, concave. Capsules small, dehiscent, glabrous; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Oxysepala, previously treated as a section within Bulbophyllum, was recently raised to generic rank (Clements and Jones (2002).
Nomenclature
Oxysepala Wight, Icon. 5(1): 17 (1851). Type species: Oxysepala ovalifolia Wight
Bulbophyllum Thouars sect. Oxysepala (Wight) Schltr.
Infrageneric Taxa: No infrageneric taxa are currently recognised.
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.