Aporopsis litoralis

Epiphytes or lithophytes with very short indiscernible rhizomes anchored by thin roots that arise from nodes at the base of the stem. The stems, which are porrect to pendulous, have a narrow base, a few swollen basal nodes and a thin, attenuated, flat apical section. The leaves, which are arranged distichously, arise from nodes along the pseudobulb. They are longer than wide, laterally flattened, often more or less triangular in shape and the basal sheath completely encloses a node. The flowers are borne 1-3 on short stalks that arise from the upper nodes of a growth. The inflorescence is perennial, can branch and produces new flowers at sporadic intervals. The basal bracts of each inflorescence are persistent and visible as a prominent tuft protruding from the node. Each flower lasts a few days and is thin to firm-textured.  The perianth segments are flat and the bases of the lateral sepals are fused with the column foot. The petals are much smaller than the sepals. The labellum, which is firmly attached to the apex of the column foot, is prominently lobed. The labellum is flared towards the apex and the ventral surface has one or more longitudinal ridges.

Significant Generic Characters

Epiphytic/lithophytic orchids; plants porrect to pendulous; stems laterally flattened throughout, thin at the base, then an expanded swollen section, then an extended leafy section with a thin leafless apical part where the flowers arise; leaves lasting several seasons, distichous, laterally flattened, entire; basal sheath enclosing a node; inflorescence short, perennial, producing flowers at sporadic intervals; inflorescence bracts persistent as prominent tufts; flowers short-lived; perianth segments thin to firm-textured; lateral sepal bases fused with the column foot; petals much smaller than the sepals; labellum firmly attached to the apex of the column foot; labellum lamina prominently lobed, flared distally; callus with longitudinal ridges.

Size and Distribution

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A genus of about 20 species distributed in the Philippines, Vanuatu, Indonesia, Solomon Islands, New Guinea and Dauan Island (925' S) in Torres Strait where there is a single non-endemic species, Aporopsis litorale.  State occurrence: Queensland (Dauan Island).

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Ecology

Aporopsis litorale grows on trees and rocks in situations of bright light, usually close to the coast. The climate is tropical and the majority of rain falls during the summer wet season (December to March), with the remaining months much drier and having sporadic or intermittent rain, particularly localised coastal showers.

Biology

Pollination: The flowers of Aporopsis litorale, which last 3-5 days, are insect-pollinated but the vector is unknown.

Reproduction: Reproduction in Aporopsis litorale is solely from seed. Seed dispersal takes 4-6 months after pollination and the capsules develop in a pendulous position. Apomixis is unknown in the genus.

Seasonal Growth: The plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.

Flowering: Flowering occurs sporadically in summer and autumn with the plants producing spasms of flowers at irregular intervals.

Hybrids: Natural hybrids involving Aporopsis litorale in Australia are unknown.

Derivation

Aporopsis means resembling Aporum, another genus related to Dendrobium (Greek -opsis, resemblance).

Botanical Description

Perennial, deciduous, epiphytic or lithophytic herbs, sympodial. Plants glabrous. Roots elongate, thin, produced from nodes on the base of the pseudobulb. Rhizome superficial, branched. Pseudobulbs absent. Stems crowded, the basal node swollen, then a short thin section followed by 2-4 enlarged and swollen nodes with an attenuated thin leafy subapical part that is flattened or terete, subtending a leafless thin section on which flowers arise; when young covered by scarious bracts. Trichomes absent. Aerial growths produced from the upper nodes, often persistent and themselves forming further aerials to produce a tangled clump. Leaves lasting several seasons, distichously arranged along the swollen part of the stems, sessile. Leaf lamina much longer than wide, thick-textured, laterally flattened with the margins fused, smooth, not grooved or channelled; base sheathing, the sheath completely enclosing a node; margins entire; apex entire. Inflorescence perennial, short, produced from the leafless upper nodes on a mature stem, usually 1-3 flowered, producing flowers at sporadic intervals, leaving a persistent tuft of bracts after each floral episode. Peduncle absent. Floral bracts scarious, small, subtending the base of the pedicel. Pedicel relatively long, thin, merging with the ovary. Ovary short, straight. Flowers resupinate, stalked, lasting several days, white, green or yellow. Perianth segments thin to firm-textured, widely spreading, entire. Dorsal sepal free, subsimilar to the lateral sepals; apex entire or cymbiformLateral sepals subsimilar to the dorsal sepal, attached by their bases to the column foot; apex cymbiform or entire. Petals free, smaller than the sepals; apex entire. Labellum continuous with the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, ecalcarate, more or less obovate, thin to fleshy; hypochile present, flat, entire; lamina expanded, three-lobed; lateral lobes entire, blunt; midlobe flared, entire or emarginate. Callus consisting of narrow parallel ridges. Nectar absent. Column lacking free filament and style, fleshy, much shorter than the perianth segments, nearly straight. Column wings present, reduced, ventral and with short tooth-like apical stelidia. Column foot well developed, much longer than the column, straight or curved. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, erostrate; apex smooth. Pollinarium absent. Pollinia 4 in 2 pairs, straight or falcate, yellow or orange, hard, waxy. Viscidium absent. Rostellum ventral, swollen, transverse. Stigma entire, transverse, concave. Capsules dehiscent, large, glabrous, pendulous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, relatively large, light coloured, winged.

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Taxonomy

Aporopsis, previously described as a subsection of section Rhopolanthe within Dendrobium, was recently raised to generic rank (Clements and Jones 2002).

Nomenclature

Aporopsis (Schltr.) M.A.Clem. and D.L.Jones, Orchadian 13 (11): 485 (2002). Type species: Dendrobium macfarlanei F.Muell. [Aporopsis macfarlanei (F.Muell.) M.A.Clem. & D.L.Jones].

Infrageneric Taxa: No infrageneric taxa are currently recognised.

References

Clements, M.A. & Jones, D.L. (2002). Nomenclatural changes in the Dendrobieae (Orchidaceae). 1: The Australasian region. Orchadian 13(11): 485-497.

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.

Schlechter, R. (1982). The Orchidaceae of German New Guinea (English translation by R.S. Rogers, H.J. Katz and J.T. Simmons). Australian Orchid Foundation, Melbourne.