Prawn Greenhood
Deciduous terrestrial orchids that reproduce both from seed and also by vegetative means to form clonal colonies. Plants are monomorphic. Sterile plants consist of a rosette of petiolate leaves similar to those on flowering plants. Flowering plants consist of a basal rosette of leaves encircling an erect central peduncle that has stem-clasping cauline leaves and a single terminal flower (rarely two). Flowers small, strongly hooded, right-way-up, green with white translucent patches and occasionally brown suffusions. Dorsal sepal and petal margins adherent to form a galea that encloses the column and part or all of the labellum. Dorsal sepal ending in a long curved filiform point. Lateral sepals are fused in the basal half to form a structure that is held erect in front of the flower, effectively closing off the flower to the outside, ending in slender terete free points that extend high above the flower. Labellum actively motile, attached basally by an elastic strap; in the set position held close to the fused part of the lateral sepals and triggered when an insect contacts its lower parts or the basal appendage; when triggered the upper part of the labellum contacts the outer surface of the column wings and closes off the lower parts of the flower. Labellum unlobed, either completely enclosed in the flower or extending above the sinus gap, with a curved basal appendage. Column gently curved, with a narrow stigma.
Similar Genera
Significant Generic Characters
Deciduous terrestrials; plants monomorphic; rosette basal, scape-encircling; flower single, small, resupinate, hooded; lateral sepals fused, erect, with long erect filamentous free tips, dorsal sepal with a long filamentous apex; labellum unlobed, with a curved penicillate basal appendage.
Size and Distribution
Crangonorchis, which consists of 2 species, is endemic in eastern Australia with a wide latitudinal distribution, extending from about 16°15' S on the Windsor Tableland in northeastern Queensland to about 43°20' S in southern Tasmania. Crangonorchis depauperata is restricted to northeastern Queensland, whereas Crangonorchis pedoglossa ranges from southeastern Queensland to southern Tasmania. Altitudinally the genus extends from sea level (Crangonorchis pedoglossa) to about 800 m alt. (Crangonorchis depauperata). State occurrence: Queensland, New South Wales, Victoria, Tasmania.
Ecology
Species of Crangonorchis are deciduous terrestrial orchids. Crangonorchis depauperata, which is restricted to northeastern Queensland, grows in well-drained sandy, gravelly or loamy soils on rainforest margins and among grass, shrubs and bracken in moist areas of open forest and woodland. Crangonorchis pedoglossa which is more widely distributed (from southeastern Queensland to southern Tasmania) grows in heathy forest, coastal scrub and heathland, in well-drained to seasonally moist or wet sandy or peaty soils.
Biology
Pollination: Both species of Crangonorchis are insect-pollinated, probably by microdipterans from the family Mycetophilidae. Very little is known about the attraction these flowers have for the insects or about the mechanisms involved, although the process is probably very similar to that outlined for Pterostylis. Neither species is autogamous and apomixis is unknown in the genus.
Reproduction: As well as reproducing from seed and in addition to forming replacement tubers, both species of Crangonorchis reproduce vegetatively by the production of daughter tubers on the end of stolonoid roots. They grow in relatively small clonal colonies.
Species of Crangonorchis take 6-10 weeks to disperse seed after pollination. There is no increase in the length of the peduncle or pedicel during this process.
Seasonal Growth: The prevailing climate where these orchids grow is seasonal. Both species exist as dormant tubers from late spring to early summer or autumn when they emerge above ground, developing a rosette and flowering soon after emergence (usually late autumn-winter). In northeastern Queensland much of the rain falls in the summer wet season and the growth of Crangonorchis depauperata is greatly influenced by this seasonality.
Flowering: Species of Crangonorchis mainly flower in autumn and winter.
Hybrids: Natural hybridisation is unknown within Crangonorchis and intergeneric hybrids are unknown.
Fire: Flowering in Crangonorchis is usually inhibited in the first season after a summer fire.
Derivation
Crangonorchis, which is based on the common name of prawn greenhood, is derived from the Greek krangon, shrimp, and Orchis, another genus of Orchidaceae but also a general term applied to orchids.
Botanical Description
Perennial geophytic herbs, sympodial. Plants vegetatively glabrous. Roots both filamentous and stolonoid. Tubers fleshy, globose; replacement tuber formed at the end of a short dropper; daughter tubers formed at the end of lateral stolon-like roots. Stem erect, short, unbranched, with membranous cataphylls at each node. Trichomes absent. Flowering and non-flowering plants monomorphic. Sterile plants consist of a rosette of petiolate leaves. Flowering plants consist of a rosette of leaves encircling a central peduncle. Leaves petiolate in a basal stem-encircling rosette; petiole narrowly winged; lamina flat; those on the scape reduced to sheathing bract -like structures. Venation acrodromus, without included veinlets. Inflorescence terminal, one-flowered (rarely two). Peduncle wiry, with closely sheathing sterile bracts. Flowers resupinate, erect, pedicellate, mostly green and white, without any noticeable scent. Nectar absent. Dorsal sepal much longer than the petals, overlapping the petal margins and adherent with them to form a galea; apex with a long filiform point. Galea with a single opening facing outwards. Lateral sepals fused in the proximal third to form an erect synsepalum; synsepalum about as wide as long, flat, closely embracing the anterior part of the galea without a lateral gap; distal parts free, each sepal ending in a free point; free points suddenly contracted and filiform, long, usually erect above the galea. Petals sessile, asymmetrical, shorter than the dorsal sepal, strongly falcate; dorsal surface much less developed than the anterior surface; dorsal flange present, deltate. Labellum free, actively motile, attached to the column foot by a short, irritable, ligulate claw; when set either fully enclosed within the flower or the tip just visible above the sinus; when triggered travelling in an arc of c. 30° and then fully enclosed within the flower. Labellum lamina entire, unlobed. Labellum basal appendage extending porrectly from the labellum base, incurved; apex penicillate. Spur absent. Callus consisting of a longitudinal ridge, half rounded in cross-section, hollow beneath. Column completely enclosed within the galea, lacking free filament and style. Column wings hatchet-shaped, fused to the column basally, distally free, two-lobed; upper margin unadorned, with a short tapered apical lobe; medial area lacking barrier trichomes; basal lobe free, the anterior margin ciliate. Column foot prominent, much shorter than the column. Pseudospur absent. Anther erect to incumbent. Pollinarium absent. Pollinia four, free, linear, soft and mealy, yellow. Stigma bilobed, medial, longer than wide, about as wide as the column. Rostellum terminal. Capsules dehiscent, erect, smooth; pedicel not elongating noticeably in fruit; peduncle not elongating in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Crangonorchis is a segregate genus from Pterostylis (Jones and Clements 2002). Its affinities are with Diplodium but morphologically it is most similar to Pterostylis from which it is basically distinguished by the short labellum enclosed within the flower and the filiform extension apex on the dorsal sepal.
Notes
Sterile plants of both species of Crangonorchis consist solely of a leafy rosette.
Nomenclature
Crangonorchis D.L.Jones and M.A.Clem., Austral. Orch. Res. 4: 67 (2002).
Type species: Crangonorchis pedoglossa (Fitzg.) D.L.Jones and M.A.Clem.
Infrageneric Taxa: No infrageneric taxa are recognised.
References
Backhouse, G. and Jeanes, J. (1995). The Orchids of Victoria. Miegunyah Press, Carlton, Victoria.
Bishop, T. (1996). Field Guide to the Orchids of New South Wales and Victoria. University of New South Wales Press, Sydney.
Clements, M.A. (1990). Catalogue of Australian Orchidaceae. Austral. Orch. Res. 1: 1-160.
Curtis, W.M. (1979). The Student’s Flora of Tasmania, Part 4A. Government Printer, Hobart.
Entwisle, T.J. (1994), in Walsh, N.G. and Entwisle, T.J. (1994). Flora of Victoria, vol. 2. Inkata Press, Melbourne.
Harden, G. (ed.) (1993). Flora of New South Wales, vol. 4. New South Wales University Press, Sydney.
Jones, D.L. (1993). Pterostylis R.Br., in G.J.Harden (ed.), Flora of New South Wales, vol. 4: 171-189.
Jones, D.L. (1994). Pterostylis R.Br., in N.G.Walsh and T.J.Entwisle (eds), Flora of Victoria, vol. 2: 798-830.
Jones, D.L. and Clements, M.A. (2002). A Review of Pterostylis, Austral. Orch. Res. 4: 3-152.
Jones, D.L. (1998). Contributions to Tasmanian Orchidology – 7: A taxonomic review of Pterostylis R.Br. in Tasmania, Austral. Orch. Res. 3: 135-177.
Jones, D.L., Wapstra, H., Tonelli, P. and Harris, S. (1999). The Orchids of Tasmania. Melbourne University Press, Victoria.
Nicholls, W.H. (1969). Orchids of Australia. Thomas Nelson, Melbourne.
Ross, E.M. and Jones, D. (1989), in Stanley, T.D. and Ross, E.M., Flora of South-eastern Queensland, vol. 3. Queensland Department of Primary Industries.
Rupp, H.M.R. (1943). The Orchids of New South Wales. Australian Medical Publishing Coy, Sydney.
Willis, J.H. (1970). A Handbook to Plants in Victoria, vol. 1 (2nd ed.). Melbourne University Press, Carlton.