Deciduous terrestrial orchids forming colonies with fleshy tubers and a single, broad, pleated glabrous or hairy leaf that is held erect or lies flat on the soil surface. The unbranched fleshy inflorescence is produced before the leaves appear and carries 1-few small to large often pendulous flowers in a terminal raceme. The sepals and petals are similar, narrow and free from each other and the labellum is usually 3-lobed and without a spur. The column is long and generally widens towards the apex.
Significant Generic Characters
Deciduous autotrophic terrestrial orchids forming colonies; tubers fleshy, subterranean; leaf solitary, appearing after the flowers, plicate, erect to horizontal, flat, glabrous or hairy, non-articulate; inflorescence racemose, terminal, appearing before the leaves; scape fleshy; flowers resupinate, small to large, often pendulous; sepals and petals free, similar, narrow; labellum 3-lobed, without a basal spur, the base embracing the column; column long, widened towards the apex.
Size and Distribution
A genus of about 80 species widely distributed in tropical areas of Africa, Madagascar, Asia, South-east Asia, Malaysia, Philippines, Indonesia, New Guinea and Australia where there are 6 species in the tropical north, 2 or 3 endemic. State occurrence: Queensland (including Moa, Saibai and Thursday Islands), Northern Territory, Western Australia.
Ecology
The native species of Nervilia grow in grassy forest and woodland, swamp margins, low-lying areas dominated by species of Melaleuca and Pandanus, on rainforest margins, in vine thickets and within patches of rainforest, especially monsoonal rainforest and littoral rainforest. Some species favour well-drained soils whereas others grow in poorly drained soils that are inundated during the wet season.
Biology
Pollination: The flowers of the native species of Nervilia are mainly insect-pollinated but the vectors are unknown.
Reproduction: Reproduction in Nervilia is mainly from seed but all the native species also produce daughter tubers and form clonal colonies. The peduncle elongates prior to seed dispersal. Apomixis is unknown in the genus.
Seasonal Growth: The native species of Nervilia are restricted to the tropics and their growth cycle is closely tied in with the wet season.
Flowering: The native species of Nervilia flower between November and January.
Hybrids: Natural hybrids are unknown in the native species of Nervilia.
Fire: Most native species of Nervilia grow in habitats that are fire-prone but the plants are dormant when the fires occur.
Derivation
The name Nervilia is derived from the Latin nervus, nerve, vein, in reference to the prominently veined leaves.
Botanical Description
Perennial geophytic herbs, autotrophic, deciduous, sympodial. Plants glabrous or pubescent, forming clonal colonies. Flowering and non-flowering plants dimorphic. Flowering plants consist of an inflorescence with a leaf arising later from a lateral growth at the base of the scape. Sterile plants consist of a single leaf. Stem tubers fleshy, subterranean, solitary, rounded, with nodes, producing short radiating roots; replacement tuber absent; daughter tubers produced on thin, fleshy, horizontal, multinoded stolons. Roots short, fleshy, unbranched. Stem short, erect, unbranched, fleshy, with 2-3 cataphylls. Trichomes present or absent, eglandular. Leaf 1 per shoot, prostrate to erect, plicate, non-articulate, entire or lobed, sessile or petiolate, as wide as long or not much longer than wide; base sheathing. Venation unknown. Inflorescence a terminal raceme, 1-few-flowered. Peduncle longer than the rhachis, fleshy, with a few closely sheathing bracts. Rhachis shorter than the peduncle, straight. Floral bracts small. Pedicel short, distinct from the ovary. Ovary straight, narrow, not twisted. Flowers resupinate, porrect to erect, relatively large, pink, purple, white, green, sometimes with a contrasting labellum, lasting 1-few days, spirally arranged, opening sequentially. Perianth segments entire, narrow, fleshy. Dorsal sepal free, subsimilar to the lateral sepals, erect to recurved. Lateral sepals free, subsimilar to the dorsal sepal, divergent. Petals free, subsimilar to the sepals, spreading. Labellum flexibly attached to the base of the column and embracing it, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina usually 3-lobed, sometimes unlobed; lateral lobes well-developed, erect and involute, column-embracing, entire; midlobe short to long, narrow to broad; margins entire, crispate or erose. Spur absent. Callus consisting of longitudinal plates, ridges or keels, glabrous or pubescent. Nectar absent. Column porrect from the end of the ovary, relatively long, narrow, straight or curved, lacking free filament and style. Column wings absent. Column foot absent. Pseudospur absent. Anther incumbent, 2-celled, persistent. Pollinariaabsent. Pollinia 2, unequal to subequal, deeply grooved, sectile, yellow. Viscidium absent. Rostellum transverse, platform-like, entire, the anterior margin protruding above the stigma. Stigma large, apical, ventral. Capsules dehiscent, glabrous, pendant; peduncle elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Notes
Species of Nervilia form clonal colonies that can be extensive and dense. Flowering plants produce an inflorescence very soon after the first heavy storms of the wet season. Floral development, capsule formation and seed dispersal is rapid and the leaves of non-flowering plants appear above ground as seed dispersal is finished. A leaf also arises from the base of the scape on flowering plants. The flowering period of some species, such as Nervilia peltata is so fleeting, that flowering plants are rarely seen in the field.
Nomenclature
Nervilia Commerson ex Gaud. In Freycinet, Voy. Uranie 421, t.35 (1829), (nom. cons.). Type species: Nervilia aragoana Gaud.
Infrageneric Taxa: No infrageneric treatment of Nervilia 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.