Helmet Orchids
Small deciduous terrestrial orchids that grow in clonal groups or colonies, usually with a very low proportion of flowering plants. Flowering plants have a single, nearly round leaf, which is often purplish beneath, and a single, squat, fleshy nearly stalkless, whitish to reddish, lantern-like, right-way-up flower sitting in the leaf base. The flower is dominated by a large hood-like dorsal sepal and labellum, with the lateral sepals and petals reduced to tiny filamentous structures at the labellum base. The base of the labellum is tubular with 2 prominent closed auricles. The main part of the labellum, which can be strongly folded or convoluted, has sharply recurved margins and is mostly enclosed within the dorsal sepal. The very short column, which is completely enclosed in the base of the labellum, has a swollen, reddish, fleshy pad on the ventral surface.
Similar Genera
Significant Generic Characters
Deciduous terrestrials; leaf single, about as long as wide, epigeous; flower single, hooded, lantern-like, resupinate; dorsal sepal greatly enlarged, sessile to subsessile, enclosing most of the labellum; lateral sepals and petals vestigial; labellum reduced, strongly folded or convolute between the tube and the shortly expanded lamina; labellum base with a pair of deflexed closed spurs; and, column squat, the anterior base expanded into a swollen, fleshy ventral pad.
Size and Distribution
A genus of about 13 species distributed in Australia, New Zealand, New Caledonia, New Guinea and Indonesia. Six species of Corybas occur in Australia and they are distributed from about 15°45' S in northeastern Queensland to about 43°10' S in southern Tasmania. State occurrence: Queensland, New South Wales (including Lord Howe Island), Victoria, Tasmania.
Ecology
Species of Corybas are deciduous terrestrial orchids that grow in clonal colonies ranging from relatively small to extensive. They are distributed from coastal and near-coastal areas to the ranges and tablelands. Corybas abellianus and Corybas cerasinus occur on the Atherton and Evelyn Tablelands up to about 1000 m alt. Habitats where Australian species of Corybas grow include heathland, open forest, grassy forest, woodland and rainforest.
Biology
Pollination: The flowers of the Australian species of Corybas are pollinated by microdipterans of the family Mycetophilidae. Commonly known as fungus gnats, the adult flies are active in humid weather, usually running or flying close to the ground and often prominent in organically rich soils. The flowers of the Australian Corybas species have a fungus-like appearance and may attract the gnats by odours, but this is speculative. Apomixis is unknown in the genus.
Reproduction: Reproduction is by seed and all species grow in clonal colonies resulting from the formation of daughter tubers on the end of long stolonoid roots. In pollinated flowers the peduncle thickens and elongates prior to seed dispersal. The period from pollination to seed shedding is about 8-10 weeks in species from temperate regions but observations suggest that it is probably 6-8 weeks in Corybas abellianus.
Seasonal Growth: Plants of Corybas are dormant over summer, surviving as small fleshy tubers and avoiding the extremes of heat, low humidity and dryness. In all species the buds emerge with the unfolding leaf and there is continued expansion of the leaves after flowering.
Flowering: Flowering mainly occurs in winter and spring. Corybas abellianus is exceptional as its growth is intimately tied in with the tropical wet season and the plants flower in mid to late summer.
Hybrids: Natural hybrids are unknown in Corybas.
Fire: Summer bushfires generally inhibit the subsequent growth and flowering of Australian species of Corybas. Severe fires may even kill a proportion of plants in a colony or can result in complete destruction of the colony.
Derivation
The generic name Corybas refers to a Corybant or dancing priest of the goddess Cybele in Phrygia.
Botanical Description
Deciduous perennial geophytic herbs, sympodial. Trichomes absent or reduced to papillae on some parts. Roots both filamentous and stolonoid. Tubers globose, paired, fleshy; replacement tuber formed at the end of a short dropper; daughter tubers formed at the end of horizontal lateral stolonoid roots. Subterranean axes, including stolonoid roots, with minute papillae, each with apical unicellular hairs. Stem erect, short, unbranched, terete, with membranous cataphylls at each node. Flowering and non-flowering plants vegetatively monomorphic. Leaf single, basal, epigeous, petiolate. Leaf lamina almost as wide as long, membranaceous to firm textured, flat, convolute in bud, hypostomatic, abaxially pellucid or with anthocyanin pigments; apex apiculate or mucronate. Venation anastomosing, the main veins uniting apically. Inflorescence terminal, 1–flowered. Peduncle fleshy, very short, lacking sterile bracts. Pedicel absent. Floral bracts foliaceous, small, semi-sheathing. Ovary elongate, erect, incurved or recurved, ribbed, glabrous. Flowers resupinate, small, fungiform or lantern-like, dull coloured (white, pink, red or purplish), epedicillate, shortly pedunculate, dominated by the dorsal sepal and labellum. Dorsal sepal free, much larger than the lateral sepals, strongly cucullate. Lateral sepals filamentous, free or united at the base, greatly reduced or vestigial, much smaller than the dorsal sepal, usually basally auriculate. Petals filamentous, free, greatly reduced or vestigial, subsimilar to the lateral sepals or even smaller, usually basally auriculate. Labellum free, attached firmly by its base to the anterior column base, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina membranaceous, not lobed, tubular in the erect proximal part then recurved or folded, the distal part shortly expanded; anterior surface smooth or papillate; margins incurved or flat, entire. Labellum base with a pair of closed auricles. Callus consisting of a thickened midline, sometimes adorned with papillae. Nectar absent. Spur absent. Column lacking free filament and style, squat, straight, with a prominent thickened reddish ventral pad or mound. Column base with lateral auricles matching the labellum auricles. Column foot absent. Pseudospur absent. Column wings mostly fused to the column, the tips free. Anther terminal, 2-celled, persistent, basifixed, erect, not rostrate. Pollinarium present, consisting of pollinia attached directly to a viscidium. Pollinia 4, unequal, mealy, yellow; pollen grains in monads or tetrads. Viscidium dorsal. Stigma entire, concave. Rostellum dorsal, transverse. Capsule dehiscent, thin-walled, ribbed; peduncle elongated and thickened in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Corybas was described in 1807 based on Corybas aconitiflorus which has labellum auricles with a closed apex. Since then the genus has been treated by most authors in a very broad sense encompassing a number of distinct natural groups, some of which have been described as separate genera. Following detailed morphological and molecular studies, Corybas was defined in the strict sense and 7 other genera were reinstated from synonymy or erected as new (Jones et al. 2002). The Australian genera included in the Corybas alliance are Anzybas, Corybas, Corysanthes and Nematoceras.
Notes
Dransfield et al. (1986), pointed out that obvious differentiating characters are lost when dried herbarium specimens are prepared or plants are stored in spirit. This applies to all members of the Corybas alliance in Australia and makes the interpretation of herbarium specimens difficult, reinforcing the importance of field studies.
Nomenclature
Corybas Salisb., Parad. Lond. t. 83 (1807). Type species: Corybas aconitiflorus Salisb.
Corysanthes R.Br. sect. Corybas (Salisb.) Endl., Gen. Pl. 1: 218 (1837).
Type species: Corybas aconitiflorus Salisb.
Infrageneric Taxa: No infrageneric taxa are recognised.
References
Dransfield, J., Comber, J.B. and Smith, G. (1986). Corybas west of Wallace’s Line: A synopsis of Corybas (Orchidaceae) in West Malesia and Asia. Kew Bulletin 41(3): 575-613.
Johns, J. and Molloy, B. (1983). Native Orchids of New Zealand. A.H. & A.W. Reed, Wellington.
Jones, D.L. (1991). New taxa of Australian Orchidaceae. Austral. Orch. Res. 2:1-207.
Jones, D.L. (1998). Contributions to Tasmanian Orchidaceae - 1: Introduction and the genera Acianthus, Arthrochilus, XClassodia, Calochilus, Corybas, Cyrtostylis, Dipodium, Dockrillia, Gastrodia, Leptoceras, Microtis, Pyrorchis and Townsonia, Austral. Orch. Res. 3: 1-15.
Jones, D.L., Clements, M.A., Sharma, I.K., Mackenzie, A.M. and Molloy, B.P.J. (2002). Nomenclatural notes arising from studies into the tribe Diurideae (Orchidaceae). Orchadian 13(10): 437-468.
Moore, L.B. and Edgar, E. (1970). Flora of New Zealand, vol. 2. Government Printer, New Zealand.
Rupp, H.M.R. (1943). The Orchids of New South Wales. National Herbarium, Sydney.
Van Royen, P. (1979). The Alpine Flora of New Guinea 2: 66-87. J. Cramer, Germany.
Van Royen, P. (1983). The genus Corybas (Orchidaceae) in its eastern areas. Phanerogamarum Monographiae Tomus XVI. J.Cramer, Vaduz.