Fairy Orchids
Epiphytes or lithophytes with indiscernible or creeping rhizomes and tufts of unusual fan-like or iris-like growths anchored by thin roots. Each growth consists of a few flattened leaves which overlap at the base and spread at the tips. Thin arching inflorescences arise from the shoot apex and carry tiny flowers, usually arranged in distinct whorls, but sometimes in a spiral. The flowers, which are carried upside-down, have tiny spreading or cupped sepals and petals and a 3-lobed labellum that usually has a small sunken pit at its base.
Significant Generic Characters
Epiphytic/lithophytic orchids; rhizomes almost indiscernible; roots thin; pseudobulbs absent; stems short to long, erect to pendulous; leaves few-several per shoot, equitant, distichous, bilaterally flattened, thin-textured but tough, longer than wide, basally sheathing, usually non-articulate, rarely articulate at the base of the lamina; inflorescence racemose, terminal, thin, multiflowered; flowers non-resupinate, lasting few-several days, tiny, dull coloured, arranged in whorls (verticels), rarely spiral; sepals and petals free, recurved to incurved; petals narrower than the petals, sometimes dentate; labellum sessile on the column, usually 3-lobed, rarely unlobed; callus consisting of a shallow pit; column very short, without a foot; pollinia 4, in 2 pairs, without stalks.
Size and Distribution
A genus of about 330 species widely distributed in tropical regions of Africa, Asia, South-east Asia, Melanesia, Malesia and Polynesia, with 7 species endemic to mainland Australia and another on Norfolk Island. The Australian species are restricted to the eastern side of the continent between the Iron Range (12°36' S) on Cape York Peninsula, Queensland and Kendall (31°38' S) in New South Wales, with a concentration in the tropics. State occurrence: Queensland, New South Wales (including Norfolk Island).
Ecology
The native species of Oberonia range from the coastal lowlands to about 900 m alt. in the ranges and tablelands of northeastern Queensland. These orchids usually grow in brightly lit situations where there is free and unimpeded air movement. Sometimes plants occur on rocks, boulders and cliff faces exposed to the full heat of the sun, but mostly they grow on the trunks and branches of rainforest trees, occasionally extending their range into drier sites. In the tropics the climate has a dominant 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 native species of Oberonia have tiny flowers but they are not self-pollinating. Capsules are produced sporadically and in groups along the racemes and the flowers are believed to by splash-pollinated by raindrops dislodging the pollen from the anthers.
Reproduction: Reproduction in Oberonia is solely from seed. Seed dispersal takes 4-6 months from pollination and the capsules develop in a porrect position. Apomixis is unknown in the genus.
Seasonal Growth: Oberonia plants grow actively in summer and autumn and are relatively quiescent for the remainder of the year.
Flowering: Flowering occurs mainly in autumn, winter and spring.
Hybrids: Natural hybrids are unknown in these orchids.
Derivation
Oberonia is named after Oberon, King of the fairies, a romantic reference by the botanist John Lindley to the tiny flowers of these orchids and their arrangement on the inflorescence.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous, consisting of 1-several fan-like or iris-like growths. Roots filamentous, thin, unbranched, produced from the base of a shoot. Stems thin, short to long, erect to pendulous. Pseudobulbs absent. Trichomes absent. Leaves 5-11 per shoot, lasting several seasons, equitant, distichous, bilaterally flattened, rarely terete (non Australian), usually non-articulate, rarely articulate at the base of the leaf lamina (non Australian). Venation unknown. Inflorescence racemose or spicate, many-flowered, erect, arcuate or pendulous, terminal. Peduncle much shorter than the rhachis, with filiform sterile bracts arranged spirally or in whorls. Rhachis much longer than the peduncle, straight, ribbed or grooved. Floral bracts small, narrow, partly sheathing. Pedicels short to vestigial, thin, merging with the ovary. Ovary short, straight, smooth. Flowers non-resupinate, tiny, usually arranged in whorls (verticels), sometimes spiral (non Australian), crowded, dull coloured (green, yellowish, orange, red or brownish), shortly pedicellate. Perianth segments tiny, free, incurved to recurved. Dorsal sepal subsimilar to the lateral sepals. Lateral sepals subsimilar to the dorsal sepal. Petals narrower than the sepals, entire or dentate/erose. Labellum fixed by its base to the anterior column base, markedly dissimilar in size to the sepals and petals, ecalcarate. Labellum lamina usually 3-lobed, sometimes unlobed (non Australian); lateral lobes small; margins entire or dentate/erose; midlobe entire or dentate/erose. Spur absent. Callus obscure, consisting of a shallow basal pit. Nectar unknown. Column very short, lacking free filament and style. Column foot absent. Pseudospur absent. Column wings relatively large, projecting or incurved, sometimes absent. Anther terminal, incumbent, shallowly concave, 2-celled, persistent, basifixed, smooth, erostrate. Pollinarium absent. Pollinia 4 in 2 pairs, crescentic or hemispherical, yellow, hard, waxy, without caudicles. Viscidium absent. Rostellum ventral, transverse, obscure. Stigma entire, concave. Capsules dehiscent, glabrous, porrect; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.
Notes
In Oberonia the first flowers to usually open on an inflorescence are those towards the middle or apex of the raceme, the flowers then opening progressively with the basal flowers opening last.
Nomenclature
Oberonia Lindley, Gen. sp. Orchid. pl. 15 (1830).
Type species: Oberonia iridifolia Lindley, nom. illeg. [Malaxis ensiformis Smith, Oberonia ensiformis (Smith) Lindl.) (type cons.).
Titania Endl., Prod. Fl. Norfolk 31 (1833). Type species: Titania miniata Endl.
Infrageneric Taxa: Schlechter (1911 & 1982) divided the genus into 2 subgenera and 10 sections. This has subsequently been modified (see Seidenfaden 1978 and Ansari and Balakrishnan 1990) but it is obvious that a detailed molecular and morphological study is needed to determine the relationships of several natural groups and whether generic limitations are more appropriate for some rather than infrageneric.
References
Ansari, R. and Balakrishnan, N.P. (1990). A revision of the Indian species of Oberonia (Orchidaceae). Orchid Monographs 4: 1-80.
Cameron, K.M. (2005). Leave it to the leaves: a molecular phylogenetic study of Malaxideae (Epidendroideae, Orchidaceae). Am. J. Bot. 92: 1025-1032.
Clements, M.A. (1989). Catalogue of Australian Orchidaceae. Austral. Orch. Res. 1: 160.
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.
Schlechter, R. (1911). Beiträge zur Kenntnis der Orchidaceen-Flora von Sumatra. Bot. Jahrb. 45: Beibl. 104: 13.
Schlechter, R. (1982 English translation). The Orchidaceae of German New Guinea, Australian Orchid Foundation.
Seidenfaden, G. (1978). Orchid genera in Thailand VII. Oberonia Lindl. & Malaxis Sol. Ex Sw. Dansk. Bot. Archiv. 33(1): 1-94.