A genus of orchids, with a single epiphytic or lithophytic species growing in tropical Australia. It has thin roots and long thin leafy stems, the leaves are flat but twisted at the base. The multi-flowered inflorescence has small cream or green stalked flowers 0.3-0.4 cm wide, that open sequentially in a spiral. The lateral sepals fuse with the column foot. The sepals are similar in size and shape while the petals are much narrower. The tiny labellum is attached to the apex of the column foot. Appendicula flower mainly between March and June, but are known to flower at other times. They occur in northeastern Queensland.
Significant Generic Characters
Epiphytic/lithophytic ort terrestrial sympodial orchids; roots thin; pseudobulbs absent; stems slender, elongate, fibrous, leafy over most of their length; leaves are arranged in 2 ranks along the stem, sheathing at the base and twisted so that all the blades lie in the same plane; racemes axillary, terminal or both, condensed to elongate, multi-flowered; flowers small, lasting 3-5 days, white or greenish; lateral sepals fused to the column foot to form a mentum; labellum obscurely- to distinctly three-lobed, stiffly attached to the apex of the column foot; column short, with a column foot; pollinia 6, in 2 groups of 3, either attached to a single common caudicle or 2 separate common caudicles fixed to a single viscidium.
Size and Distribution
A genus of about 60 species occurring in China, India, Sri Lanka, Southeast Asia, Malaysia, the Philippines, Indonesia, Polynesia, New Guinea and Australia where there is a single species, Appendicula australiensis in northeastern Queensland between the McIlwraith Range (27º05’S) on Cape York Peninsula and Tully (17°56’S). State occurrence: Queensland.
Ecology
Species of Appendicula grow on trees and rocks in moist to wet forests, especially rainforest, often close to streams and waterfalls. Plants commonly grow in shady humid situations where there is free and abundant air movement.
Biology
Pollination: The flowers of Appendicula species are tiny and relatively short lived. Little is known about their pollination syndrome. Some species seem to be self-pollinating, but the native species seems to be insect pollinated.
Reproduction: Reproduction in Appendicula is solely from seed. Seed dispersal takes 2-4 months from pollination and the capsules develop in a porrect position. Apomixis is unknown in the genus.
Seasonal Growth: Appendicula plants grow actively in summer and autumn and are relatively quiescent for the remainder of the year.
Flowering: Appendicula australiensis flowers mainly March to June, but can flower sporadically at other times.
Hybrids: Natural hybrids are unknown in these orchids.
Derivation
The name Appendicula is derived from the Latin appendicula, little appendix, in reference to the inward-facing appendages on the labellum.
Botanical Description
Perennial, evergreen, epiphytic, lithophytic, rarely terrestrial (non-Australian) herbs, sympodial. Plants glabrous. Rhizome superficial. Roots filamentous, thin. Pseudobulbs absent. Stems clustered, simple or branched, thin, terete or laterally flattened, fibrous, erect or pendulous, leafy over most of their length. Trichomes absent. Leaves lasting several seasons, distichous, flat, twisted at the base so all the laminae lie in the same plane, thinly coriaceous; base sheathing; apex emarginate. Venation unknown. Inflorescence racemose, terminal (non-Australian), lateral or both, elongate or condensed, multi-flowered. Peduncle similar to or longer than the rhachis, thin, with scattered sterile bracts. Rhachis thin, straight, sometimes condensed. Floral bracts narrow, sheathing. Pedicels short, merging with the ovary. Ovary short, straight, smooth. Flowers resupinate, small, crowded, white or greenish, stalked, opening sequentially in a spiral. Perianth segments short, relatively broad. Dorsal sepal free, similar to the lateral sepals, porrect to recurved. Lateral sepals fused at the base to the margins of the column foot to form a mentum, similar to the dorsal sepal, porrect to spreading. Petals smaller than the sepals, spreading. Labellum stiffly attached to the apex of the column foot, markedly dissimilar in size to the sepals and petals, ecalcarate. Labellum lamina obscurely- or distinctly three-lobed (non-Australian), sessile, broad; base saccate; lateral lobes flat or incurved; midlobe porrect to decurved, sometimes with a median ridge (non-Australian). Spur absent. Callus basal, round, concave or forming keels (non-Australian), usually pointing towards the labellum base. Nectar present or absent. Column short, lacking free filament and style. Column foot present. Pseudospur formed by the saccate labellum base and mentum. Column wings short, apical. Anther terminal, incumbent, 2-celled, persistent, basifixed, rostrate. Pollinarium present. Pollinia 6 in 2 groups of 3, clavate, orange, stalked, either attached to a single common caudicle or 2 separate common caudicles fixed to a single viscidium. Viscidium narrow. Rostellum ventral, elongate. Stigma entire, concave. Capsules dehiscent, small, glabrous, porrect; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
The Australian species was included in Podochilus for many years. (Clements and Jones 1992).
Nomenclature
Appendicula Blume, Bijdr. 6: t.5; 7: 297 (1825). Type species: not designated.
Infrageneric Taxa: Appendicula has been subdivided into sections but further study is needed (see Schlechter 1982).
References
Clements, M.A. and Jones, D.L. (1992). New combinations in Appendicula Blume and Octarrhena Thwaites (Orchidaceae) in Australia. Phytologia 73(2): 117-118.
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.