A large genus of approximately 70 species, Thelymitra are commonly known as sun orchids because the flowers of most species open on hot sunny days and close again at night. These plants are ground orchids with a single leaf at the base of the flower stem, which is channelled and usually long and narrow but can also be short and broad. The flower stem is unbranched and has multiple flowers, each with a short stalk. The flower is star shaped and approximately 1 to 5 cm wide. Flower colour varies and may occur as a single colour or as a pattern. Thelymitra flowers are unusual in that all flower parts look similar, making it hard to distinguish the labellum from the petals. The column protrudes conspicuously from the centre of the flower and can be colourful and adorned with prominent hair tufts. Flowering usually occurs in spring and summer, though a couple of species flower in winter. The genus in widespread, and occurs across Australia except in the Northern Territory.
Significant Generic Characters
Deciduous terrestrial orchids; leaf single, erect, usually longer than wide, straight or spirally twisted; raceme multiflowered; flowers resupinate, nearly actinomorphic, opening in response to sunlight and heat, brightly coloured (blue, purple, pink, red or yellow); sepals and petals similar or subsimilar; labellum unlobed, similar or subsimilar to the petals and sepals; callus absent; column prominent, central, broadly winged; lateral lobes (column arms) prominent, adorned with papillae, trichomes or lobes.
Size and Distribution
A genus of more than 120 species distributed in Australia, New Zealand, including Stewart Island, Chatham Island and Auckland Island, New Caledonia, New Guinea, Indonesia and the Philippines. Although Thelymitra has its greatest proliferation in southern Australia and New Zealand, the genus itself is much more widespread than this and has elements distributed from subantarctic islands to the tropics. Latitudinally Thelymitra is distributed from about 15° N in the Philippines to about 50° S on Auckland Island. In eastern Australia the genus is distributed from the Big Tableland (c. 15º45' S) near Cooktown in northeastern Queensland to about 43º S in southern Tasmania. In Western Australia the genus is distributed between about 27º S and 35º S. State occurrence: Queensland, New South Wales, Victoria, Tasmania, South Australia, Western Australia.
Thelymitra species occur in a wide range of mesic habitats from coastal situations to montane and alpine zones up to about 1500 m alt. Habitats in Australia include slopes and ridges in sclerophyll forest and woodland, coastal scrubs developed on tertiary sands and calcareous sand, heathland, sandplain vegetation, mallee shrubland over sheet limestone, clefts and crevices in sandstone outcrops, sphagnum hummocks, particularly in subalpine regions, moist to wet swamps, subalpine meadows and bogs. Various species also frequently colonise track verges and road embankments.
Species of Thelymitra are commonly known as sun orchids because the perianth segments of most species expand on hot sunny days, closing again at night. Observations in the field and on cultivated plants show that the higher the diurnal temperature the more rapidly the flowers open and the wider the resulting expansion of the perianth segments. In some species these even recurve away from the column on very hot days leaving the column protruding prominently. On days of high humidity the perianth segments expand more readily and at lower temperatures than on drier days. Response to temperature varies with the taxon and some species are very reluctant to open their flowers fully even in hot weather, whereas others may expand readily even on relatively cool days.
Thelymitra flowers are different from most other orchids in that the labellum lacks any ornamentation or calli and it is not greatly differentiated in shape and size from the petals. As a result the flowers approach radial symmetry which is unusual in the Orchidaceae. The role of pollen vector attraction belongs to the column rather than the labellum. This structure has a well-developed mitra formed by the fusion of the two lateral staminodes and the filament of the fertile stamen (Burns-Balogh & Bernhardt 1985). This mitra surrounds the anther and stigma and may form an expanded apical hood or it may extend as a rim-like collar. Either structure can be colourful and ornamented with calli, ridges or papillae. Also present are protruding column arms that support clusters of trichomes or are themselves expanded like lobes, toothed or sculptured. Auxiliary lobes may also be present in some species between the column arms and the mitra rim.
The basic pollination syndrome in Thelymitra involves deceit and floral mimesis (Bernhardt & Burns-Balogh 1986, Dafni & Calder 1987). Some species are totally entomophilous relying completely on cross-pollination, whereas others are facultatively or obligatorily autogamous (Fitzgerald 1875-1895, Cheeseman 1881, Bates 1978, Cropper and Calder 1990). Many species originating on mountain tops and in colder climates expand tardily if at all with cleistogamy being common in such areas.
The pollinarium of Thelymitra consists of two pairs of white pollinia attached directly to an elliptical or ovoid viscidium. In the strictly entomophilous cross-pollinating species, the pollen grains are tightly packed and the pollinia retain their integrity and attachment to the viscidium unless exposed to air. By contrast, in the autogamous species the pollen grains are loosely packed and the pollinia break down and become incoherent prior to or during early anthesis. The pollinia also frequently separate from the viscidium so that the whole pollinarium cannot be extracted as a single unit. Any pollen that comes into contact with stigmatic fluid germinates and can bring about auto-fertilisation. In such autogamous species the perianth segments may not expand at all, even in hot weather. This is especially true of species or variants from montane regions where cool cloudy conditions are frequent during the period of anthesis.
As to be expected, sporadic hybridisation can occur between entomophilous, cross-pollinating species of Thelymitra. Perhaps surprisingly it can also occur between autogamous taxa during periods when the weather is sufficiently hot for the perianth to expand. Usually this latter hybridisation is a result of female Lassioglossum (Halictidae) bees transferring fragments of pollinia to the stigma of another species while foraging for pollen (Jones & Clements 1998). For an excellent summation of pollination mechanisms in Thelymitra see Bower 2001.
Reproduction: Most species grow as individuals or in loose groups and reproduce solely from seed. A few species produce extra replacement tubers to form localised tufts (such as Thelymitra gregaria) or develop daughter tubers on the end of stolonoid roots to form clonal colonies (T. antennifera, T. cyanea). Seed dispersal takes 8-12 weeks after pollination. Apomixis is unknown in the genus.
Seasonal Growth: These orchids occur in seasonal climates and have periods of active growth and dormancy, the latter coinciding with times of low humidity, heat and dryness.
Flowering: Flowering of Thelymitra occurs mainly over spring and summer, with T. hiemalis and T. apiculata being unusual in their winter flowering period.
Hybrids: Hybridisation appears to be relatively frequent in Thelymitra (McCrae and Molloy, 1998) and there is evidence of speciation occurring via this process (Molloy and Dawson,1998; Peakall and Molloy, 1998). (see also pollination notes above).
Fire: Species from open habitats generally flower regularly in the absence of fire, but as the vegetation increases in density so flowering is reduced and summer burns may have a promoting effect. This is especially true of some habitats such as heathland and forests with a heathy or shrubby understorey. Some species of Thelymitra, such as Thelymitra antennifera, respond positively to a summer burn and flower freely in the following spring.
Perennial geophytic herbs, sympodial. Roots filamentous. Tubers ovoid to obovoid, paired, fleshy, naked; replacement tubers formed on the end of short droppers, sometimes extra daughter tubers formed in the same manner, rarely daughter tubers formed on the end of stolonoid roots. Stem erect, short, unbranched, terete, with membranous cataphylls at each node. Leaf single, basal, erect, convolute, flat or conduplicate, sessile. Leaf lamina usually much longer than wide, flat, canaliculate or terete, straight or rarely twisted spirally, often thick and fleshy and ribbed dorsally, glabrous or rarely hairy. Inflorescence racemose, 1-many-flowered, erect, terminal. Peduncle fleshy or wiry, sometimes flexuose, smooth. Sterile bracts 1-4 (rarely more), foliaceous. Floral bracts foliaceous, sheathing the pedicel, margins usually free, sometimes basally connate. Pedicels slender to stout, smooth. Ovary elongate, ribbed, glabrous. Flowers resupinate, nearly actinomorphic, brightly coloured (blue, purple, pink, red or yellow), often blotched, spotted or veined, pedicellate, the perianth parts usually spreading in response to warm humid diurnal conditions, opening freely or tardily, insect-pollinated, autogamous or cleistogamous. Perianth segments thin-textured, dull or shiny. Sepals free, usually all similar or the dorsal sepal broader, valvate or imbricate. Petals free, similar or dissimilar to the sepals, valvate or imbricate. Labellum free, attached by its base to the anterior column base, usually similar in shape and size to the sepals and petals, sometimes broader or narrower, ecalcarate. Labellum lamina not greatly differentiated from petals, not lobed, unadorned, the margins entire or undulate. Callus absent. Nectar absent. Column lacking free filament and style, fully exposed when the flower is open, broadly winged. Column wings fused and surrounding the column; basal anterior part of wings forming an unadorned rim or ridge in front of the stigma base; apical part of wings often extending above the anther to form a mitra; dorsal apical part of mitra complex, 3-5-lobed, usually tripartite with a central post-anther lobe (midlobe) and two lateral lobes (column arms), sometimes extra auxiliary lobes or lobules flank the post-anther lobe on the anterior side; post-anther lobe prominent or reduced, in one group elongate, tubular, cucullate and hooding the anther, variously cleft, lobed or toothed apically, often differently coloured from the rest of the column, in another group much reduced and dorsally adorned with digitiform calli or papillae; lateral lobes digitiform or flat, erect or porrect, straight, curved or sharply bent, distally adorned with trichomes, papillae or lobes. Column foot absent. Anther basifixed, 2-celled, erect, inclined or porrect, rostrate or not. Pollinarium present, consisting of pollinia attached directly to a viscidium. Pollinia 4, in 2 pairs, clavate, white, soft, mealy; pollen grains in monads or tetrads, coherent in entomophilous species, loose and friable in autogamous species. Viscidium terminal or dorsal, circular to elliptic. Stigma entire or bilobed, situated basally and supported on a thick stalk. Rostellum ventral. Capsules dehiscent, glabrous, erect; pedicels not elongating in fruit; peduncle not elongating in fruit. Seeds numerous, light or dark coloured, winged.
Thelymitra is placed in the tribe Diurideae, subtribe Thelymitrinae. The flowers of most species have the ability to open and close depending on daylight and temperature.
1. Thelymitra J.Forst. and G.Forst., sect. Thelymitra. Flowers of uniform colouration, rarely spotted; post-anther lobe forming a terminal hood; column arms with prominent trichomes. Type species: Thelymitra longifolia J.Forst. and G.Forst.
3. Thelymitra J.Forst. and G.Forst., sect. Macdonaldia Benth., Fl. Aust. 6: 317 (1873). Flowers of uniform colouration; post-anther lobe not forming a terminal hood; column arms expanded into a flattish lobe, lacking trichomes. Type species: Thelymitra smithiana (Gunn ex Lindl.) Benth.
4. Thelymitra J.Forst. and G.Forst., sect. Biaurella Benth., Fl. Aust. 6: 317 (1873). Flowers in a range of metallic hues; post-anther lobe not forming a terminal hood; column arms expanded into ellipsoid or cylindrical lobes, lacking trichomes. Type species: Thelymitra variegata (Lindl.) F.Muell.
Backhouse, G. and Jeanes, J. (1995). The Orchids of Victoria. Miegunyah Press, Carlton, Victoria.
Bernhardt, P. and Burns-Balogh, P. (1986). Floral mimesis in Thelymitra nuda (Orchidaceae). Pl. Syst. Evol. 151: 187-202.
Bernhardt, P. (1993). In Flora of New South Wales, vol. 4. (ed. G. Hardin), pp. 146-152, New South Wales University Press, Sydney.
Bishop, T. (1996). Field Guide to the Orchids of New South Wales and Victoria. University of New South Wales Press, Sydney.
Clements, M.A. (1989). Catalogue of Australian Orchidaceae. Austral. Orch. Res. 1: 1-160.
Cropper, S.C. and Calder, D.M. (1990). The floral biology of Thelymitra epipactoides (Orchidaceae), and the implications of pollination by deceit on the survival of this rare orchid. Plant Syst. & Evol. 170: 11-27.
Hatch, E.D. (1952). The New Zealand forms of Thelymitra J.R. and G.Forster. Trans. Roy. Soc. New Zealand 79: 386-398.
Jeanes, J.A. (2000). Two new species of Thelymitra (Orchiaceae) from southeastern Australia. Muelleria 14: 91-97.
Jeanes, J.A. (2004). Resolution of the Thelymitra canaliculata R.Br. (Orchidaceae) complex in southern Australia. Muelleria 15: 75-89.
Jeanes, J.A. (2004). A revision of the Thelymitra pauciflora R.Br. (Orchidaceae) complex in Australia. Muelleria 19: 19-79.
Jones, D.L. and Clements, M.A. (1998). Contributions to Tasmanian Orchidology - 8: A Taxonomic Review of Thelymitra J.R. & G. Forst. in Tasmania. Austral. Orch. Res. 3: 178-203.
McCrae, D.P. and Molloy, B.P.J. (1998). The artificial reconstruction of the natural New Zealand hybrid Thelymitra X dentata (Orchidaceae). New Zealand J. Bot. 36: 121-125.
Molloy, B.P.J. and Dawson, M.I. (1998). Speciation in Thelymitra (Orchidaceae) by natural hybridism and amphiploidy. New Zealand J. Bot. 36: 103-113.
Moore, L.B. (1969). Taxonomic notes on New Zealand monocotyledons. New Zealand J. Bot. 6: 473-492.
Nicholls, W.H. (1969). Orchids of Australia. Thomas Nelson, Melbourne.
Peakall, R. and Molloy, B.P.J. (1998). Isozyme evidence for the amphidiploid origin of Thelymitra decora (Orchidaceae). New Zealand J. Bot. 36: 115-117.
Ross, E.M. and Jones, D. (1989). In Flora of South-eastern Queensland, Vol. 3. (ed. T.D. Stanley. and E.M. Ross), pp. 390-394, Queensland Department of Primary Industries, Brisbane.
Rupp, H.M.R. (1943). The Orchids of New South Wales. Australian Medical Publishing Coy, Sydney.
Weber, J.Z. and Bates, R. (1986). In Flora of South Australia. 4th ed. (ed. J.P.Jessop and J.P.Toelken), pp. 2132-2145, South Australian Printing Division, Adelaide.
Weber, J.Z. and Entwisle, T.J. (1994). In Flora of Victoria, vol. 2. (ed. N.G.Walsh, N.G. and T.J. Entwisle), pp. 840-854, Inkata Press, Melbourne.
Willis, J.H. (1970). A Handbook to Plants in Victoria vol. 1 (2nd ed.). Melbourne University Press, Carlton.