Eucosia umbrosa

Jade Orchids

Terrestrials with succulent, above-ground, creeping stems with an erect apex, anchored by wiry roots that appear woolly.  The relatively large, broad leaves, which arise in a basal to central rosette, are thin-textured, petiolate, light green and often shiny. Spikes terminal on a shoot, hairy. Flowers crowded, right-way-up, dull-coloured, not hairy. Dorsal sepal and petals overlapping to form a hood. Lateral sepals widely divergent. Labellum attached to the anterior base of the column, projecting forwards, concave and resembling a basin, the surface with numerous irregular soft awl-shaped structures.

Similar Genera

Salacistis

Significant Generic Characters

Terrestrial orchids; rhizomes succulent, above-ground, creeping with an erect apex, anchored by wiry nodal roots that appear woolly; leaves petiolate, in a basal to central rosette, glabrous, relatively broad, thin-textured, shiny, light green; inflorescence spicate, terminal on a shoot; flowers resupinate, relatively large, crowded, dull-coloured (green, brownish reddish, pinkish), glabrous; dorsal sepal and petals overlapping to form a galea; lateral sepals widely divergent. Labellum attached to the anterior base of the column, obscurely lobed, without a spur; hypochile much larger than the epichile, the base broadly pouched, ornamented with numerous, irregularly arranged, soft, subulate unicellular papillae; epichile reduced, entire. Stigma concave, bilobed, with the lobules fused and with raised margins.

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Size and Distribution

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A genus of c.15 species distributed in tropical regions from northern India and Japan south to Malaysia and east to New Guinea, Solomon Islands, New Caledonia, Polynesia and Australia. A single endemic species, Eucosia umbrosa, occurs in northeastern Queensland, more or less between Mt Finnigan (1548' S) and Mt Fox (1850 S).  State occurrence: Queensland.

Ecology

Eucosia umbrosa grows in friable soil, litter and humus in sheltered humid positions in highland rainforest. It also grows in cracks and crevices on large granite boulders and in accumulated litter on large rocks and boulders in sheltered gullies close to streams. Elevation ranges from about 700 m to 1400 m alt. The climate has a summer wet season (December to March) with the remaining months being much drier with sporadic or intermittent rain.

Biology

Pollination: The flowers of Eucosia umbrosa are insect-pollinated. A species of small fly is the probable vector.

Reproduction: Eucosia umbrosa reproduces solely from seed. Seed dispersal takes 3-4 months from pollination and the capsules develop in an erect position. There is no elongation of the peduncle or pedicels. Apomixis is unknown in the genus.

Seasonal Growth: Eucosia umbrosa survives the dry parts of the year as leafy quiescent plants.

Flowering: Eucosia umbrosa flowers between June and August.

Hybrids: Eucosia umbrosa does not participate in natural hybridisation.

Fire: Eucosia umbrosa does not grow in fire-prone habitats.

Derivation

Eucosia is derived  from the Greek, eu, well and kos, ornament, an apparent reference to the ornamental flowers.

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Botanical Description

Perennial, evergreen, terrestrial herbs, sympodial. Roots wiry, produced from rhizome nodes, appearing woolly from a covering of root hairs. Rhizome cylindrical, fleshy, unbranched or sparsely branched, prostrate. Stem erect, usually 1 shoot per plant, similar to the rhizome. Pseudobulbs absent. Trichomes present on peduncle, rhachis, bracts and ovaries, unbranched, multiseriate, eglandular. Leaves lasting 1-2 seasons, few per shoot, spirally arranged, petiolate, sheathing at the base, glabrous, forming a loose rosette. Leaf lamina longer than wide, asymmetric, thin, membranaceous, flat, smooth, entire, light-coloured. Venation acrodromus to campylodromus, with cross-veinlets and few anastomoses. Inflorescence spicate, terminal on a growth, few-flowered, erect. Peduncle longer than the rhachis, pubescent, with semi-sheathing to projecting, glabrous or pubescent sterile bracts.  Floral bracts sheathing, glabrous or pubescent. Ovary elongate, projecting at an angle from the rhachis, straight, twisted, pubescent. Flowers resupinate, crowded, opening widely, dull coloured (green, pink, brownish or reddish), usually glabrous, sessile to subsessile. Dorsal sepal closely overlapping the petals to form an upright galeaLateral sepals free, usually widely divergent, occasionally porrect. Petals of similar length to the sepals, forming a galea with the dorsal sepal, strongly asymmetric, membranousLabellum fixed by its basal margins to the anterior margins of the column base, immoveable, projecting forwards like a basin, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina obscurely divided into a hypochile and an epichile; hypochile much larger than the epichile, entire, with a broad pouched base, ornamented proximally with numerous, irregularly arranged, soft, subulate unicellular papillae; epichile sessile, short, plain; apex entire. Callus consisting of 2 low flat keels that extend to the labellum apex.  Nectar absent. Column lacking free filament and style, narrow, elongated, dilated below the middle. Column wings vestigial. Column foot absent. Pseudospur absent. Anther dorsal, 2-celled, erect, persistent, basifixed, with an extended rostrum. Pollinarium present. Pollinia 2, clavate, deeply grooved, straight, yellow, sectile, attenuated into stalks that attach to the viscidium. Viscidium present, linear-oblong to attenuate. Rostellum short, narrow. Stigma medial, bilobed, lobules fused, concave, with raised margins. Capsules dehiscent, pubescent, erect, often with persistent floral parts; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.

Taxonomy

Within the subtribe Goodyerinae Eucosia is distinguished by the resupinate flowers, simple basin-like labellum without a spur, ornamented with soft, subulate papillae, pollinia attenuated into basal stalks and stigma bilobed with the lobules fused and with raised margins.

Eucosia is included within Goodyera in most modern floras but molecular studies show conclusively that both genera are distinct and Eucosia should be reinstated.

Notes

The native species, which has been linked with Goodyera viridiflora Blume, was described as Eucosia umbrosa by Jones and Clements (2004).

Nomenclature

Eucosia Blume, Bijdr., 415; Tab. 1, fig. 18 (1825).  Type species: Eucosia carnea Blume.

Infrageneric Taxa: No infrageneric taxa are recognised.

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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.

Jones, D.L. and Clements, M.A. (2004). Miscellaneous new species, new genera, reinstated genera and new combinations in Australian Orchidaceae. Orchadian 14(8): Scientific Supplementi-xvi.

Pridgeon, A.M., Cribb, P.J., Chase, M.W. and Rasmussen, F.N. (eds), (2003). Genera Orchidacearum, Vol. 3. Oxford University Press.