Grass Orchids
A small genus with a single evergreen terrestrial species that is grassy in appearance. It has wiry roots with small fleshy tubers attached. Growing in sheltered forested areas, these orchids have narrow fibrous erect stems with numerous spirally arranged leaves. The sparsely or non-branched inflorescence has flowers that are also arranged in a spiral. The small flowers measuring 0.8-1.2 cm in width are yellow and star-shaped. The sepals and petals are narrow with a small tooth-like structure at the tip. The labellum is similar to the sepals and petals. Apostasia occur in northeastern Queensland and flower in the wet season over summer.
Significant Generic Characters
Evergreen terrestrial orchids; roots thin, wiry, with small fleshy tubercles; stems thin, wiry, emergent; leaves numerous, thin, sessile, non-articulate, sheathing at the base; inflorescence axillary, racemose or sparsely branched; flowers small, stellate; sepals and petals very similar, narrow, ridged or keeled dorsally, ending in a small cusp; column organs incompletely fused; filaments fused basally, distally free; stamens 2 or 3, the median stamen sterile (staminodial) or absent; anthers with one or both margins fused, clasping the style; style base fused with the base of the filaments, distally free; pollen present as monads; capsule indehiscent, disintegrating when ripe.
Size and Distribution
A genus of about 7 species distributed in China, the Ryukyu Islands, northeastern India, Sri Lanka, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, the Philippines, Indonesia, New Guinea and Australia where there is a single endemic species, Apostasia stylidioides, in northeastern Queensland between Bamaga (10º53’ S) and Ingham. (18°39’S). State occurrence: Queensland.
Ecology
Apostasia grows in sheltered forested areas in moist to well-drained soils, including sand, gravelly loam, clay loam and loam. Plants occur in a range of situations from dense shade to forest margins, sometimes close to streams. Habitats include several types of rainforest from the coast to the ranges and tablelands and wetter types of open forest.
Biology
Pollination: The flowers of Apostasia are self-pollinating. Some exotic species are pollinated by bees that vibrate the anthers to release the pollen.
Reproduction: Reproduction in Apostasia is solely from seed. Seed dispersal takes 8-12 months from pollination and the capsules develop in an erect position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Apostasia are evergreen and grow mainly during the spring and summer months.
Flowering: Apostasia flowers in summer (wet season).
Hybrids: Natural hybrids involving Apostasia are unknown.
Fire: Apostasia sometimes grows in fire-prone habitats. The above-ground parts of the plants are destroyed by fire and reshoot from subterranean parts of the stem.
Derivation
The name Apostasia is derived from the Greek apostasia, separation, divorce, and refers to the distinct floral features which suggest that the genus is distinct from most other orchids.
Botanical Description
Perennial geophytic herbs, evergreen, sympodial. Plants glabrous. Flowering and non-flowering plants monomorphic. Roots filamentous, wiry, ramiferous, bearing fleshy mycorrhizal tubercles. Stems erect, emergent, thin, wiry, ligneous, multi-noded, with scale-like bracts at each node, unbranched or sparsely branched. Trichomes absent. Leaves many per shoot, spirally arranged, non-articulate, lasting many years, thin-textured, coriaceous, sheathing at the base. Venation simple, parallel. Inflorescence racemose or sparsely branched, axillary, arcuate or pendulous. Peduncle much shorter than the rhachis, thin, wiry, sparsely bracteate. Rhachis longer than the peduncle, straight. Floral bracts narrow, scarious. Pedicel indistinct. Ovary straight, not twisted, narrow, often erect. Flowers non-resupinate, spirally arranged, small, more or less erect, stellate, not crowded, white (non-Australian) or yellow, lasting a few days, opening sequentially. Perianth segments , including labellum, similar, free, spreading, the tips cymbiform. Sepals 3-5-nerved, with a thick ridged dorsal midrib that ends in a subulate cusp. Petals 1-3-5-nerved, sessile or stalked, with a fleshy, keeled dorsal midrib that ends in a subulate cusp. Labellum lamina simple, unlobed, unadorned. Spur absent. Callus absent. Nectar unknown. Column porrect from the end of the ovary, formed by the fusion of the lower portion of the style, the base of the filaments and the staminode (if present), the upper parts of the filaments and style free; stamens 2 or 3, the median stamen sterile (staminodial) or absent; anthers with one or both margins fused, clasping the style. Column wings absent. Column foot absent. Pseudospur absent. Pollinarium absent. Pollinia absent. Pollen present as monads. Stigma terminal, entire or lobed. Capsules erect, indehiscent, disintegrating when ripe; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, dark coloured, stalked, with a minute apical appendage, sticky when dry.
Taxonomy
Apostasia has a number of floral features not consistent with Orchidaceae in the strict sense and some authors place the genus in the Apostasiaceae. Genetic studies however place them as a primitive group within the Orchidaceae and they are placed in the subgenus Apostasioideae.
Notes
Plants of Apostasia stylidioides have wiry roots with small fleshy tubercles attached. These structures probably have some limited storage capacity for moisture and nutrients but their main role is as a site of symbiosis with mycorrhizal fungi.
The Australian species has been included by many authors within Apostasia wallichii R.Br. That species however grows much larger than Apostasia stylidioides with longer, broader leaves and larger flowers.
Nomenclature
Apostasia Blume, Bijdr. 6: fig. 39; 8: 423 (1825). Type species: A. odorata Blume.
Niemeyera F.Muell., Fragm. Phyt. Austr. 6: 96 (1867). Type species: N. stylidioides F.Muell.
Adactylus (Endl.) Rolfe, Orchid Rev. 4: 329 (1896). Type species: Apostasia nuda R.Br.
Infrageneric Taxa: A genus of 2 sections -
1. Section Apostasia de Vogel, Blumea 17(2): 336 (1969). Type species: A. odorata Bl. Flowers with a staminode.
2. Section Adactylus Endl.,Gen. Pl., part 3: 221 (1837). Type species: A. nuda R.Br. Flowers without a staminode.
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.
Wood, J.J. (1999), Apostasia in Pridgeon, A.M., Cribb, P.J., Chase, M.W. and Rasmussen, F.N. (eds), Genera Orchidacearum, Vol. 1. Oxford University Press.