Dove Orchid
Coarse epiphytes with projecting fibrous stems upturned at the apex and broad, drooping leaves with prominent parallel veins and distinctively hooked tips. Inflorescences are long, thin, unbranched with numerous, small, crowded, fragrant flowers. They have relatively narrow incurved segments and a thin labellum that is hinged to the apex of the column foot. The column is relatively long and sharply curved with a relatively short column foot.
Significant Generic Characters
Moniliform epiphytic orchids; plants moderately large, porrect with an upturned apex; stems thick, fibrous; leaves large, well-spaced, in 2 ranks, longer than wide, thin-textured, leathery; venation parallel, prominent; apex hooked, unequally notched; inflorescence racemose; flowers small, numerous, lasting several days; perianth segments thin-textured, incurved; sepals and petals subsimilar; labellum hinged to the apex of the column foot; lamina obscurely 3-lobed, with a short broad basal spur; lateral lobes erect; midlobe vestigial, fleshy; column short, sharply recurved near the middle, with a short foot; pollinia 4, stalked on a stipe, in 2 subequal pairs.
Size and Distribution
A monospecific genus with the single species, Peristeranthus hillii, endemic in eastern Australia and distributed between ranges south of Cooktown (about 15º45' S) and Port Macquarie (about 31º27' S) in northern New South Wales. In temperate and subtropical regions the plants are mainly found at low to moderate altitudes but in the tropics they are restricted to moderate or high altitudes in the ranges and tablelands. State occurrence: Queensland, New South Wales.
Ecology
Peristeranthus hillii grows at low, moderate or high altitudes on shrubs and trees in rainforest (including littoral rainforest), streamside vegetation and wetter types of open forest.
Biology
Pollination: The flowers of Peristeranthus hillii last many days, contain nectar and are pollinated by a small beetle, Metriorrhynchus rufipennis, in the family Lycidae (Wallace 1980, Forster 1988).
Reproduction: Reproduction in Peristeranthus hillii is solely from seed. Seed dispersal takes 10-12 months after pollination and the capsules develop in a porrect position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Peristeranthus hillii grow mainly during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Peristeranthus hillii flowers in winter and early spring.
Hybrids: Natural hybrids involving Peristeranthus hillii are unknown.
Derivation
Peristeranthus, which is derived from the Greek peristera, dove and anthos, flower, refers to the column apex which resembles a dove’s head.
Botanical Description
Perennial, evergreen, epiphytic herbs, monopodial. Roots relatively thin, elongate, straight or convolute, adherent. Plants moderately large, porrect with an upturned apex. Stem relatively thick, short to moderately long, fibrous, sparsely branched. Pseudobulbs absent. Trichomes absent. Leaves lasting several seasons, well-spaced, distichous, sessile, longer than wide, mostly flat, thinly coriaceous, smooth; base sheathing the stem, persistent after leaf abscission; margins entire; apex uncinate, unequally emarginate. Venation parallel, prominent. Inflorescence lateral, racemose, arcuate to pendulous, multiflowered. Peduncle shorter than the rhachis, wiry, with basal imbricate scarious bracts. Rhachis straight. Floral bracts scarious, sheathing the base of the pedicel. Pedicel short, thin, merging with the ovary. Ovary short, straight. Flowers resupinate, small, stalked, opening sequentially, facing the tip of the raceme, lasting several days, green with red markings, fragrant. Perianth segments thin-textured, incurved. Dorsal sepal free, subsimilar to the lateral sepals. Lateral sepals subsimilar to the dorsal sepal, the bases partially joined to the column foot, flanking the labellum. Petals free, subsimilar to the sepals. Labellum hinged to the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, calcarate. Labellum lamina fleshy, with a basal spur, obscurely 3-lobed; spur short, broadest laterally, with thick walls, notched, with a narrow erect finger-like callus structure on the distal wall; lateral lobes large, deltate, erect, with a curved point; midlobe vestigial, fleshy. Spur (see labellum lamina). Callus (see labellum lamina). Nectar unknown. Column relatively long, porrect from the apex of the ovary, sharply incurved near the middle, lacking free filament and style, fleshy. Column wings obscure, ventral. Column foot short, continuous with the column. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, smooth, with a narrow curved rostrum. Pollinarium present. Pollinia 4 in 2 appressed pairs, subequal, orange, hard, waxy, stalked. Stipe well-developed, elongate, narrow. Viscidium large, broad, at an angle to the stipe. Rostellum short, decurved, bifid. Stigma large, entire, concave. Capsules dehiscent, glabrous, porrect; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Within the Vandeae, Peristeranthusis characterised by large leaves with prominent parallel venation and hooked tips; hinged, obscurely 3-lobed labellum; short broad spur with an erect, narrow, apical callus structure; short (vestigial) fleshy midlobe; short column with a short foot and, 4 stalked pollinia in 2 subequal pairs.
Nomenclature
Peristeranthus Hunt, Queensland Naturalist. 15: 17 (1954).
Type species: Saccolabium hillii F.Muell. [Peristeranthus hillii (F.Muell.) Hunt].
References
Dockrill, A.W. (1967). Australasian Sarcanthinae. The Australasian Native Orchid Society, Sydney.
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.
Forster, P.I. (1988). Pollination of Peristeranthus hillii by Metriorrhynchus rufipennis (Coleoptera: Lycidae). The Coleopterists Bulletin 42(2): 166.
Wallace, B. (1980). Canthorophily and the pollination of Peristeranthus hillii. Orchadian 6: 214-215.