Epiphytes or lithophytes with prominent pseudobulbs, either clustered or well separated by a rhizome. Pseudobulbs fleshy, with several nodes, when young covered by brown papery bracts. Leaves 1-3 per pseudobulb, apical, firm-textured to fleshy, longer than wide, flat. Racemes relatively short, arising from the side or near the apex of a pseudobulb. Flowers lasting several days, relatively small, often hairy, usually cup-shaped, sometimes not opening at all. Lateral sepal bases fused with the column foot. Petals smaller than the sepals. Labellum hinged to the apex of the column foot or the column base. Labellum lamina usually 3-lobed, rarely unlobed, usually with longitudinal ridges or keels.
Similar Genera
Significant Generic Characters
Epiphytic/lithophytic orchids; rhizomes very short or creeping; pseudobulbs fleshy, multinoded; leaves lasting several seasons, 1-3 per pseudobulb, apical, duplicate, firm-textured and tough, sometimes fleshy, longer than wide, flat, articulated on the apex of the sheathing base; racemes arising from lateral or subapical nodes of a pseudobulb, relatively short, multiflowered; peduncle and rhachis circular in cross-section, not winged; flowers lasting few days, relatively small, cupulate, sometimes cleistogamous; perianth segments often pubescent; lateral sepal bases fused with the column foot; petals smaller than the sepals; labellum hinged to the apex of the column foot or the column base, obscurely winged; lamina 3-lobed, rarely unlobed, thin-textured; callus with central keels or ridges.
Size and Distribution
A genus of about 150 species widely distributed in Asia, South-east Asia, Malaysia, Philippines, Indonesia, New Guinea and Polynesia with 4 in Australia, 3 endemic. The native species are restricted to Queensland between the Iron Range (12º38’ S) on Cape York Peninsula and Mt Elliot (26º06’ S) near Ayr. State occurrence: Queensland, Western Australia (Christmas Island).
Ecology
The native species of Bryobium are restricted to tropical Queensland where they grow on trees and rocks in sheltered humid sites with free air movement. They commonly grow in moist to wet rainforest, on trees overhanging streams and in mist and cloud forest at high elevations. The majority of rain falls during the summer wet season (December to March) with the remaining months being drier with sporadic or intermittent rain.
Biology
Pollination: The flowers of the native species of Bryobium are generally short-lived and autogamous or cleistogamous, although Bryobium intermedium appears to be insect-pollinated.
Reproduction: Reproduction in Bryobium is solely from seed. Seed dispersal takes 2-4 months after pollination and the capsules develop in an erect position. Apomixis is unknown in the genus.
Seasonal Growth: The plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Flowering occurs mainly between August and December but sporadic flowering can occur at other times.
Hybrids: Natural hybrids involving species of Bryobium are unknown.
Derivation
Bryobium is derived from the Greek bryon, moss and bios, life, an apparent reference to the plant habit and/or epiphytic habit.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants hirsute. Roots elongate, filamentous, very thin, branched, produced from nodes on the base of the pseudobulb. Rhizome variable, from superficial (Bryobium irukandjianum) to well-developed and creeping (Bryobium eriaeoides), branched. Pseudobulbs well-developed, multinoded, fleshy, either crowded (Bryobium irukandjianum) or widely-spaced (Bryobium eriaeoides), short to relatively elongate, when young covered by brown scarious bracts. Trichomes present on various parts. Aerial growths absent. Leaves lasting several seasons, terminal, 1-3 per shoot, distichous, duplicate, sessile or petiolate, longer than wide, firm textured, coriaceous, smooth, flat, not grooved or channelled, articulate on the apex of the sheathing base; base sheathing the pseudobulb; margins entire; apex unequally emarginate. Inflorescence racemose, mainly short, erect to arcuate, arising from a lateral or subapical node on a mature pseudobulb, multiflowered. Peduncle shorter, equal to or longer than the rhachis, cylindrical in cross-section, glabrous or pubescent, with scattered scarious bracts. Floral bracts scarious, sheathing the base of the pedicel. Pedicel relatively short, thin, cylindrical, merging with the ovary, usually pubescent. Ovary short, straight, non-twisted, porrect from the pedicel, usually pubescent. Flowers resupinate, stalked, lasting 1-few days, white, cream or pinkish, sometimes not opening. Perianth segments thin to thick-textured, incurved to widely spreading, entire, flat to concave, glabrous or pubescent externally. Dorsal sepal free, subsimilar to the lateral sepals; apex entire, flat. Lateral sepals subsimilar to the dorsal sepal, straight or falcate, attached by their bases to the column foot to form a mentum; apex entire. Petals free, generally smaller than the sepals; apex entire. Labellum hinged to the apex of the column foot or the base of the column, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina usually 3-lobed, rarely unlobed (Bryobium irukandjianum); lateral lobes, if present, relatively large, erect, flanking the column or incurved, entire; midlobe short, porrect to decurved apex entire or apiculate. Spur absent. Callus consisting of narrow, median, parallel ridges, rarely absent (Bryobium irukandjianum). Nectar absent. Column at an angle to the end of the ovary, lacking free filament and style, fleshy, shorter than the perianth segments, nearly straight. Column wings obscure, lateral, sometimes with short tooth-like apical stelidia. Column foot small to well developed, sometimes vestigial (Bryobium irukandjianum). Pseudospur absent. Anther terminal, incumbent, small, 8-celled, persistent, attached dorsally by a ligulate claw, smooth, erostrate or with a short rostrum. Pollinarium present, consisting of pollinia attached by caudicles, sometimes with a rostellum. Pollinia 8 in 2 groups of 4, orange, hard, waxy, stalked. Viscidium small or absent. Rostellum ventral, swollen, transverse. Stigma entire or bilobed, transverse, concave. Capsules dehiscent, glabrous or hairy, erect; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Bryobium was recently reinstated as distinct from Eria based on thin filamentous roots, pseudobulbs of several nodes, each node with a papyraceous bract, leaves with obscure venation, racemes arising from lateral and subapical nodes, racemes with a cylindrical peduncle and rhachis, cupulate flowers with blunt segments and narrow column with obscure wings.
Nomenclature
Bryobium Lindl., Nat. Syst. (ed 2), 446 (July ?1836), nom. nud.; in Edwards’s Bot. Reg. 24 (Misc.): 79 (Oct. 1838). Type species: Bryobium pubescens Lindl.
Infrageneric Taxa: Bryobium is a complex genus which requires a detailed study to elucidate infrageneric and generic relationships.
References
Brieger, F.G. (1981). Subtribus Dendrobiinae. In F.G. Brieger, R. Maatsch and K. Senghas (eds), Rudolph Schlechter, Die Orchideen: ihre Bescreibung, Kultur und Züchtung, 3rd edn, Band 1, Teil A, Lieferung 11-12 (Paul Parey: Berlin and Hamburg).
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.