Australian Tropical Rainforest Orchids
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Arthrochilus sabulosus

Spotted Elbow Orchid

Arthrochilus sabulosus D.L.Jones, Austral. Orch. Res. 2: 11-12, f. 11 (1991). Type: Queensland; Horn Island, ca 4.5 km west of airstrip towards jetty, 1035S, 14215E, 9 Feb 1989, D.L. Jones 3558, B. Gray, P.S. Lavarack and J.R. Clarkson (holo CANB; iso BRI, CANB, MEL, NSW).

Distribution

Occurs in far north Queensland on Horn Island in Torres Strait and on Cape York Peninsula.

Altitude: 0-100 m.

Description

Terrestrial herb forming spreading colonies. Sterile plants a basal rosette of leaves only. Fertile plants an inflorescence with a rosette encircling base of inflorescence. Leaves 2-3, prostrate, basal, ground-hugging, ovate to lanceolate, 1-3.5 cm x 0.6-1.5 cm, dull green above, paler and shiny beneath, margins entire or undulate, apex acute to ubacute. Inflorescence a terminal raceme, erect, 120-370 mm tall, very slender, green; pedicels obliquely erect, 2 mm long. Flowers 3-15, non-resupinate, erect to porrect, 10-15 mm long, pale green with reddish to brownish labellum glands. Dorsal sepal free, decurved, embracing basal quarter of column, widest near apex, linear to tapered when flattened, 10-12 mm x 2 mm, margins conduplicate, apex obtuse with short dorsal ridge. Lateral sepals reflexed against the ovary, falcate, lanceolate, 7.5-8 mm x 2 mm, distal margins conduplicate, apex obtuse to slightly emarginate. Petals reflexed against the ovary, falcate, linear, 8-9 mm x 1 mm, distal margins conduplicate, apex obtuse. Labellum free, recurved, 6 mm x 0.8 mm, hinged to the underside of the column foot by a claw 0.1 mm long, base purple, 2.2 mm wide, becoming pale green along length, apex obtuse. Callus insectiform, proximally fused to lamina, 4.5 mm long; central area with crowded, shiny, clubbed calli 0.6-1 mm long, reddish to brownish; apex broadly emarginate, 1.5 mm wide, appearing spotted, with shiny black glands. Column incurved in a semi-circle, 9 mm long, light green, inner surface shortly pubescent, with 2 pairs of column wings; proximal column wings, 4 mm x 5 mm, broadly triangular, projecting forwards, translucent with few purple spots, apex linear to filiform; distal wings smaller, linear to tapered, falcate, 2.5 mm x 0.5 mm, divergent above anther. Column foot 3 mm long, apex anvil-shaped. Capsules erect, obovoid, 9 mm x 3.5 mm, dehiscent.

Ecology

Occurs mainly in 'Epacrid Scrub', a vegetation dominated by tree-like Leucopogon species growing on deep, coarse-grained sand dunes. It occurs less frequently on poorly drained sites typically dominated by Pandanus species.

Locally common.

Flowering period: November-February.

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