Evergreen terrestrials with thin fibrous stems carrying broad, thin-textured, pleated leaves in the upper half. Congested branched inflorescences with crowded white flowers arise in the upper axils. The upside-down flowers are relatively large, with narrow curled or wavy sepals and petals and an unusual labellum which has a narrow tubular basal part and an expanded heart-shaped blade with crinkled margins. The basal part of the labellum lies in close proximity to the long narrow column.
Similar Genera
Significant Generic Characters
Evergreen terrestrial orchids; roots thin, wiry, unbranched; stems long, thin, wiry, fibrous, unbranched; leaves broad, plicate, sessile, non-articulate, sheathing at the base; inflorescence a condensed, corymbose axillary panicle; flowers non-resupinate, large, crowded; sepals and petals narrow, subsimilar, curled or wavy; labellum fixed to the column base; lamina with a long, narrow, semi-tubular hypochile forming a pseudospur with the column and a broadly flared epichile with irregular to crenate margins; callus consisting of narrow ridges, sometimes ending in small callosities; column long, narrow.
Size and Distribution
A genus of about 5 species distributed in Africa, India, Sri Lanka, Thailand, Malaysia, Philippines, Indonesia, New Guinea, Polynesia and Australia where there is a single non-endemic species, Corymborkis veratrifolia, in northeastern Queensland between Iron Range (12º38’ S) and Airlie Beach. (20°16’ S). It also occurs in Malaysia, Indonesia and New Guinea and extends to Christmas Island. State occurrence: Queensland, Western Australia (Christmas Island).
Ecology
Corymborkis veratrifolia grows in shady humid areas of lowland rainforest, often on slopes near streams, in well-drained soil that is often rich in humus. In some areas plants extend to moderate altitudes on the ranges and tablelands.
Biology
Pollination: The flowers of Corymborkis veratrifolia are believed to be pollinated by moths that hover in front of the flowers during late afternoon and evenings, feeding on the nectar.
Reproduction: Reproduction in Corymborkis veratrifolia is solely from seed. Seed dispersal takes 6-8 months from pollination and the capsules develop in a porrect position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Corymborkis veratrifolia are evergreen and grow mainly during the spring and summer months.
Flowering: Corymborkis veratrifolia flowers in summer (wet season).
Hybrids: Natural hybrids involving Corymborkis veratrifolia are unknown.
Fire: Corymborkis veratrifolia does not grow in fire-prone habitats.
Derivation
The name Corymborkis is derived from the Greek korymbos, cluster, and Orchis another genus of orchid but also a general term used for an orchid; the name refers to the corymbose inflorescence of these orchids.
Botanical Description
Perennial geophytic herbs, evergreen, sympodial. Plants glabrous. Flowering and non-flowering plants monomorphic. Roots filamentous, wiry, generally unbranched, without tubercles. Rhizomes subterranean, stem-like, each section ending in a stem. Stems erect, emergent, unbranched, wiry, fibrous, multinoded, the nodes in the proximal half with closely sheathing scale-like bracts, distal nodes each bearing a leaf. Trichomes absent. Leaves several per shoot, more or less distichous, plicate, non-articulate, lasting many years, thin-textured, coriaceous, sheathing at the base. Venation simple, parallel. Inflorescence a condensed corymbose panicle, axillary. Peduncle much shorter than the rhachis, thick, wiry, sparsely bracteate. Rhachis longer than the peduncle, thin, wiry, curved. Floral bracts narrow, scarious. Pedicel indistinct. Ovary straight or curved, not twisted, narrow. Flowers non-resupinate, clustered, relatively large, crowded, white or greenish, lasting a few days, all flowers in a cluster opening more or less together. Perianth segments narrow, subsimilar, irregularly curled, undulate. Dorsal sepal free, longer than the lateral sepals, straight. Lateral sepals free, shorter than the dorsal sepal, strongly curved. Petals similar to the dorsal sepal and shorter than the lateral sepals, dilated distally, tips often recurved. Labellum free, stiffly attached to the base of the column, the basal part parallel to and closely embracing the column, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina divided into a hypochile and epichile; hypochile long, narrow, closely embracing the column and forming a pseudospur; epichile expanded suddenly, with irregularly undulate to crenate margins. Spur absent. Callus consisting of low ridges on the epichile, sometimes ending in small callosities, sometimes extending onto the epichile as lines. Nectar present. Column porrect from the end of the ovary, long and narrow, straight, lacking free filament and style, fleshy. Column wings terminal. Column foot absent. Pseudospur present (see labellum lamina). Anther dorsal, contiguous with the column, 2-celled, persistent, with a long rostrum. Pollinarium present. Pollinia 2, narrow, grooved, sectile, attached by a short to long common caudicle. Viscidium well-developed. Rostellum projecting past the apex of the anther, triangular, deeply bifid. Stigma terminal, broad, with 2 lateral arms. Capsules dehiscent, glabrous, porrect; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Notes
Corymborkis veratrifolia usually has a defined flowering period however in wet years successive inflorescences can be produced from succeeding nodes up the stem resulting in an extended flowering period.
Nomenclature
Corymborkis Thouars, Nov. Bull. Sci. Soc. Philom. Paris1: 518 (1809). Type species: Corymborkis corymbis Thouars.
Corymbis Thouars, Orch. Hist. Pl. Orchidees 1: tt. 37-38 (1822).
Infrageneric Taxa: No infrageneric treatment of Corymborkis is available.
References
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.