Zeuxine oblonga

Jewel Orchids

Deciduous terrestrials with succulent, above-ground, creeping rhizomes with an erect apex, anchored by wiry roots that appear woolly.  The relatively narrow dark green leaves, which arise in a basal to central rosette, are thin-textured and stalked or stalkless. Spikes short to long, terminal on a shoot, hairy. Flowers small, wider than long, right-way-up, dull-coloured, glabrous or sparsely hairy. Dorsal sepal and petals overlapping to form a hood. Lateral sepals overlapping the labellum base. Labellum attached to the anterior base of the column, with a broad pouched base and broad and entire or deeply cleft apical lobe. Basal pouch with 1-few (often 2) large stalkless glands.

Significant Generic Characters

Terrestrial orchids, deciduous; rhizomes succulent, above-ground, creeping with an erect apex, anchored by wiry nodal roots that appear woolly; leaves sessile or petiolate, in a central rosette, glabrous, relatively narrow, thin-textured, dark green; inflorescence spicate, short, terminal on a shoot; flowers resupinate, small, often short-lived, dull-coloured (green, reddish, white), externally glabrous or hairy; dorsal sepal and petals overlapping to form a galea; lateral sepals enclosing the labellum base. Labellum attached to the anterior base of the column, with a deep saccate base; hypochile tapered with a narrow apical neck; epichile entire or deeply bilobed, with 2 large entire lobes. Basal spur with 1-few (often 2) large stalkless glands. Column short, with 2 stigmas and long rostellar arms.

Size and Distribution

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A genus of about 50 species distributed in tropical regions from Africa to Asia, South-east Asia, Malesia, Melanesia, Polynesia, New Caledonia and Australia. A single widespread species, Zeuxine oblonga, extends to mainland Australia and another species, Zeuxine exilis, is endemic on Christmas Island. Zeuxine oblonga is distributed from at least as far north as the Iron Range (1238 S) on Cape York Peninsula, Queensland, south to near Coffs Harbour in New South Wales (3018' S).  State occurrence: Queensland (including Moa Island), New South Wales, Western Australia (Christmas Island).

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Ecology

Species of Zeuxine usually grow among litter in dark moist forests, particularly rainforest, in areas where there is constant high humidity. Zeuxine oblonga also grows near seepage areas and swamps and often colonises road verges and track margins. Elevation ranges from sea level to about 1000 m alt.

Biology

Pollination: The flowers of Zeuxine oblonga are probably insect-pollinated. The pollinarium has a distinct viscidium and the stigmas are well-developed as if for cross-pollination. Nothing is known about the pollination of Zeuxine. exilis.

Reproduction: Zeuxine reproduces solely from seed. Seed dispersal takes 2-3 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: Zeuxine oblonga survives the dry parts of the year as leafless quiescent plants.

Flowering: Both Zeuxine oblonga and Zeuxine exilis flower between July and September.

Hybrids: Zeuxine oblonga does not participate in natural hybridisation.

Fire: Zeuxine oblonga does not grow in fire-prone habitats.

Derivation

Zeuxine is derived  from the Greek, zeuxis, fusing, yoking, an apparent reference to the partially fused column and labellum and possibly also referring to the pollinia.

Botanical Description

Perennial, deciduous, 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, apical, usually 1 shoot per plant, similar to the rhizome. Pseudobulbs absent. Trichomes present on peduncle, rhachis, bracts, ovaries and the exterior of the sepals, unbranched, multiseriate, eglandular. Leaves lasting 1 season, few per shoot, spirally arranged, sessile or shortly petiolate, sheathing at the base, forming a loose rosette. Leaf lamina longer than wide, thin, membranaceous, glabrous, flat, smooth, entire, dark green. Venation acrodromus to campylodromus, with cross-veinlets and few anastomoses. Inflorescence spicate, terminal on a growth, erect, few-many-flowered. Peduncle longer than the rhachis, hirsute, with sheathing, hirsute sterile bracts.  Floral bracts sheathing, hirsute. Ovary elongate, asymmetric, twisted, straight or curved, hirsute. Flowers resupinate, small, crowded, dull coloured (sepals green to reddish, petals and labellum white), sessile, externally hirsute or glabrous. Dorsal sepal closely overlapping with the petals to form a galeaLateral sepals free, porrect to divergent, enclosing the labellum base. Petals of similar length to the sepals, membranous, forming a galea with the dorsal sepal, strongly asymmetric.  Labellum fixed by its basal margins to the anterior margins of the column base, its base enclosed by the lateral sepals, immoveable, markedly dissimilar in size and shape to the sepals and petals, calcarate. Labellum lamina divided into a hypochile and an epichile; hypochile equal to or longer than the epichile, entire, tapered distally, with a pouched base containing 1-few stalkless smooth glands on each side; epichile sessile; apex entire or deeply bilobed, the lobes large, entire, vertical or spreading. Callus obscure.  Nectar absent. Column short, lacking free filament and style. Column wings absent or vestigial, marginal. Column foot absent. Pseudospur absent. Anther dorsal, 2-celled, persistent, basifixed, with an acuminate rostrum. Pollinarium present. Pollinia 2, clavate, curved, yellow, sectile, fused directly to a viscidium or attached via a common stalk. Viscidium present. Rostellum ventral, elongate, deeply bilobed and forming 2 arm-like structures. Stigmas 2, separate, situated on the apical corners of the column. Capsules dehiscent, hirsute, erect; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.

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Taxonomy

Within the subtribe Goodyerinae, Zeuxine can be recognised by the resupinate hairy flowers, saccate labellum with 1-few (often 2) stalkless glands and unwinged column.

Notes

Zeuxine exilis has not been seen since 1904 and must be considered to be critically endangered or even extinct.

Nomenclature

Zeuxine Lindl., Coll. Bot. Appl. No 18 (1825).  

Type species: Zeuxine sulcata (Roxb.) Lindl. [Pterygodium sulcatum Roxb].

Infrageneric Taxa: No infrageneric taxa are recognised in this treatment.

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.

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

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