Giant Climbing Orchid
Terrestrial orchids with robust climbing stems that are greenish in colour and have large leaf-like bracts at the base of each branch. Branches on the upper parts of the stems produce panicles that carry numerous relatively large colourful flowers. Each flower is short-lived but they are produced in succession from each panicle. The flowers, which are up the right way, are yellow with pink to red or orange markings on the labellum. The sepals and petals spread widely and the large colourful labellum is ornamented with thick simple or branched papillae and hairs. The column lacks a column foot.
Similar Genera
Significant Generic Characters
Robust terrestrial orchids with long, green, branching, climbing stems; large green leaf-like bracts subtend each branch, the upper branches forming multiflowered panicles; flowers relatively large, colourful, expanding widely, short-lived, opening in sequence; perianth segments of similar length, free, the petals narrower than the lateral sepals; labellum with a short, narrow, tubular hypochile and a broadly expanded semicircular epichile, the ventral surface bearing thick simple or branched papillae and multicellular trichomes; callus consisting of ridges or keels; column narrow, curved, obscurely winged, without a column foot.
Size and Distribution
A genus of about 8 species distributed in Indonesia, New Guinea, Fiji, Ternate Island, Moluccas and Australia where there is a single non-endemic species, Pseudovanilla foliata, distributed sporadically between the McIlwraith Range (13°34’ S) on Cape York Peninsula, Queensland and Kempsey (31°05’ S) in northern New South Wales. State occurrence: Queensland, New South Wales.
Ecology
Most species of Pseudovanilla grow in wet tropical or subtropical forests. They have specific ecological requirements and because they rely for survival on an intimate association with fungi and wood in a suitable stage of decay, they are usually found in sites following disturbance, such as forests damaged by cyclones or logging. Sometimes the death of a single large tree will be sufficient to allow plants to establish. The adult orchid plants are capable of limited photosynthesis via their green stems and foliaceous bracts but rely heavily on the fungus for nutrition. The plants are active as long as their fungal food source is present but quickly decline and disappear when the source collapses.
Biology
Pollination: The flowers of Pseudovanilla foliata are fragrant and pollinated by native bees.
Reproduction: Pseudovanilla foliata reproduces solely from seed. Seeds are dispersed 10-12 months after pollination and the capsules develop in a pendulous position. Apomixis is unknown in the genus.
Seasonal Growth: The stemsof Pseudovanilla foliata last above ground for at least 12 months to mature any capsules that have been formed. A new flush of stems is produced from the base of the plant in late winter and spring.
Flowering: Pseudovanilla foliata flowers sporadically between October and February. The buds reach a certain stage of development and remain quiescent before opening rapidly following an environmental stimulus. Each flower lasts 1-2 days.
Hybrids: Natural hybridisation involving Pseudovanilla foliata is unknown.
Fire: Plants of Pseudovanilla foliata mostly occur in habitats that are not prone to fire.
Derivation
The generic name is derived from the Greek pseudes, false and Vanilla another genus of Orchidaceae, in reference to similarities with that genus.
Botanical Description
Perennial leafless geophytic herbs with climbing stems, sympodial. Plants glabrous. Roots thick, fleshy, appressed to the host, branched. Stems monopodial, thick, erect, elongate, climbing, branched, green. Leaves absent, reduced to triangular scale-like bracts at each node. Inflorescence a multibranched panicle terminating an axillary shoot, multiflowered. Peduncle wiry, about as long as the rhachis or longer, glabrous. Sterile bracts small to large, sometimes foliaceous, sometimes green. Rhachis condensed, straight. Floral bracts reduced and scale -like. Pedicels long, merging with the ovary. Ovary elongate, virtually indistinguishable from the pedicel, smooth. Flowers resupinate, opening widely, pale coloured (greenish or yellow) with a large ornate labellum, pedicellate. Perianth segments spreading, fleshy. Dorsal sepal free, subsimilar to the lateral sepals. Lateral sepals free, subsimilar to the dorsal sepal, divergent. Petals free, narrower than the sepals. Labellum basal margins fused to the apical margins of the column to form a pseudospur, dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina divided into a hypochile and epichile; hypochile basal, short, narrow, tubular; epichile broadly expanded, semicircular; ventral surface covered with thick columnar, simple or branched papillae and multicellular trichomes; margins undulate/crispate. Callus consisting of 2 fleshy medial ridges. Nectar unknown. Spur absent. Column elongate, narrow, incurved, lacking free filament and style. Column foot absent. Pseudospur present (see labellum). Column wings obscure. Anther terminal, 2-celled, persistent, basifixed, with a short rostrum. Pollinarium absent. Pollinia 2, curved, soft, mealy or powdery, granular, yellow, deeply grooved. Viscidium absent. Rostellum ventral. Stigma entire, concave. Capsules dehiscent, elongate-cylindric, glabrous, pendulous; pedicels not elongating in fruit; peduncle not elongating in fruit. Seeds numerous, large, circular, winged, the wing with a basal cleft.
Taxonomy
Pseudovanilla was originally included in Galeola but is more closely related to Vanilla (Garay 1986).
Notes
Pseudovanilla foliata is a vigorous saprophytic species that can produce stems to about 15 m long. These stems have a monopdial habit and are attached to the host by flattish roots that have an unusual branching pattern.
Nomenclature
Pseudovanilla Garay, Bot. Mus. Leafl. 30: 223 (1986). Type species: Pseudovanilla foliata (F.Muell.) Garay.
Infrageneric Taxa: No infrageneric treatment of Pseudovanilla is available.
References
Clements, M.A. (1990). Catalogue of Australian Orchidaceae. Austral. Orch. Res. 1: 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.
Garay, L.A. (1986). Olim Vanillaceae. Bot. Mus. Leaflets (Harvard Uni.) 30: 223-237.