Ghost Orchids
Leafless terrestrials with rootless wrinkled subterranean rhizomes and erect, brittle, pale, fleshy, hollow scapes which carry pendant cream, yellowish or pinkish stalked semitubular flowers in a terminal raceme. The top of the inflorescence nods in bud and flower and becomes erect in fruit. The flowers are very short-lived with free sepals and petals and a deeply concave labellum with a prominent basal spur. The column is short and broad without a column foot.
Significant Generic Characters
Leafless mycotrophic terrestrial orchids; rhizomes fleshy, subterranean, wrinkled, horizontal, without roots; inflorescence racemose, terminal; peduncle fleshy, pale, brittle, hollow; flowers semitubular, cream, yellowish or pinkish; sepals and petals free; labellum flexibly attached to the base of the column; lamina unlobed, deeply concave, with a prominent basal spur; column footless; stigma basal; pollinia 2, sectile, attached by a long caudicle to a viscidium.
Size and Distribution
A genus of 3 species widely distributed and occurring in Europe, Africa, India, Japan, Malaysia, Indonesia, New Guinea with a single widespread species, E. roseum, extending to Australia and distributed between the Windsor Tableland in northeastern Queensland and the Macleay River in northern New South Wales. State occurrence: Queensland, New South Wales.
Ecology
Epipogium roseum lives in symbiotic association with a mycorrhizal fungus in areas where there is rotting wood at a suitable stage of decay to support the fungus. It commonly occurs in high rainfall forest, particularly rainforest and wet sclerophyll forest, but also occurs in drier forests and grassland. The inflorescence nods in bud and during flowering and straightens and elongates prior to seed dispersal.
Biology
Pollination: The flowers of Epipogium roseum are self-pollinating.
Reproduction: Reproduction in Epipogium roseum is solely from seed although the plants often grow in tufts or clumps and there may be limited vegetative increase. Seed dispersal takes 7-14 days from pollination and the capsules develop in a porrect to pendant position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Epipogium roseum survive as subterranean rhizomes with the inflorescence the only part to emerge above ground.
Flowering: Epipogium roseum flowers December to March.
Hybrids: Epipogium roseum is not known to participate in natural hybridisation.
Fire: Epipogium roseum sometimes occurs in fire-prone habitats but the plants are dormant at the time of burning.
Derivation
The name Epipogium is derived from the Greek epi, upon, and pogon, beard, in reference to the labellum supposedly resembling a beard.
Botanical Description
Perennial, leafless, geophytic herbs, mycotrophic, sympodial. Plants glabrous. Rhizomes fleshy, subterranean, elongate, irregularly shaped, wrinkled, with rhizoids, mostly horizontal, lasting many years. Roots absent. Stem absent. Trichomes absent. Leaves absent. Inflorescence a terminal raceme, few-many-flowered. Peduncle much longer than the rhachis, thick, fleshy, hollow, brittle, yellowish. Sterile bracts tubular, sheathing. Rhachis shorter than the peduncle, apex nodding at anthesis, erect in fruit. Floral bracts small, spreading. Pedicel short, distinct from the ovary. Ovary straight, smooth, conspicuously swollen. Flowers resupinate or non-resupinate, crowded, semitubular to campanulate, cream, yellowish or pinkish, pendulous, very short-lived, opening sequentially in a spiral. Perianth segments thin-textured, smooth. Dorsal sepal free, similar to the lateral sepals, porrect. Lateral sepals free, similar to the dorsal sepal, slightly divergent. Petals free, subsimilar to the sepals. Labellum flexibly attached to the base of the column, markedly dissimilar in size and shape to the sepals and petals, calcarate. Labellum lamina unlobed, with a prominent basal spur, thin-textured, deeply concave and enclosing most of the column; apex decurved. Spur oblong to cylindric, directed backwards. Callus consisting of 2 glandular ridges, sometimes papillate distally, sometimes rows of calli or basal calli. Nectar absent. Column porrect from the end of the ovary, very short, relatively broad, sometimes gibbous dorsally, fleshy, lacking free filament and style. Column wings absent. Column foot absent. Pseudospur absent. Anther very large, fleshy, incumbent or erect, erostrate. Pollinarium present, consisting of viscidium, caudicle and pollinium. Pollinia 2, ovate, sectile, yellow, with 2 upturned elongate caudicles projecting in front of the anther. Viscidium ovate. Rostellum ventral, flat, entire, triangular. Stigma basal, horizontal, entire. Capsules dehiscent, smooth, porrect to pendulous; peduncle elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Epipogium has some unusual morphological features particularly in the column with its large fleshy anther attached by its posterior surface and the horizontal stigma situated at the column base.
Notes
This orchid is only above ground for 1-2 weeks each year and is readily missed.
Nomenclature
Epipogium Gmelin ex Borkhausen, Tent. Disp. Pl. German. 139 (1792). Type species: Satyrium epipogium L. [Epipogium aphyllum Sw.].
Galera Blume, Bijdr. 6: t.1, f.3; 8: 415 (1825) Type species: Galera nutans Blume.
Ceratopsis Lindl., Gen. sp. orchid. Pl. 383-4 (1840). Type species: Limodorum roseum D.Don.
Podanthera Wight, Icon. Pl.Ind. Orch. 5, t. 1759 (1852). Type species: Podanthera pallida Wight.
Infrageneric Taxa: There has been no formal division of Epipogium into infrageneric taxa.
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.