Australian Tropical Rainforest Orchids
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Arthrochilus latipes

Robust Elbow Orchid

Arthrochilus latipes D.L.Jones, Austral. Orch. Res. 2: 8-9, f. 7 (1991). Type: Northern Territory: Radon Gorge, Mt Brockman, 1245S, 13253E, 7 Dec 1978, C.R. Dunlop 5044 (holo DNA, iso DNA).

Distribution

Occurs in the Northern Territory, chiefly in western Arnhem Land.

Altitude: 50-300 m.

Description

Terrestrial tuberous herb forming spreading colonies. Sterile and flowering plants dimorphic.Sterile plants a basal rosette of leaves only. Fertile plants an inflorescence with a rosette arising later from lateral stem at base of peduncle. Leaves 2-4, prostrate, ground-hugging, basal; lamina lanceolate, 2.5-7.5 cm x 0.8-2.6 cm, green, paler beneath, margin entire or undulate, apex acute to acuminate. Inflorescence a terminal raceme, erect, 100-300 mm long, green, fleshy; pedicels obliquely erect, 2 mm long. Flowers 3-15, non-resupinate, erect to porrect, 15-25 mm long, green with brownish labellum glands, each flower lasting more than 12 hours. Dorsal sepal free, decurved, narrowly obovate to spathulate, embracing basal quarter of column, 13-15 mm x 3-4 mm, margins conduplicate, apex broadly obtuse. Lateral sepals reflexed against the ovary, lanceolate, falcate, 10-11 mm x 3-5 mm, distal margins conduplicate, apex obtuse to slightly emarginate. Petals reflexed against the ovary, linear, falcate, 10-11 mm x 1 mm, distal margins conduplicate, apex obtuse. Labellum free, recurved, 7.5 mm x 1.5 mm, hinged to underside of column foot by claw 0.3 mm long, base purplish, 3 mm wide. Callus insectiform, proximally fused to lamina, 5 mm x 3 mm; central area with crowded, shiny, clubbed calli 0.5-1 mm long, yellowish brown to brown; apex bulbous, 2 mm wide, nearly straight, with shiny black glands. Column incurved in a semi-circle, 10 mm long, inner surface shortly pubescent, with 2 pairs of column wings; proximal column wings projecting forwards, triangular, 4 mm x 6 mm; distal wings smaller, narrowly triangular, 2.8 mm x 0.8 mm, divergent above anther. Column foot 3.3 mm long, apex anvil-shaped. Capsules erect, ovoid, 10 mm x 4 mm, dehiscent.

Ecology

Occurs mainly on the sheltered slopes of sandstone escarpments, often growing under Allosyncapria ternata, and forming spreading clonal colonies. It is also found in monsoon forests and in moist areas of open forests, commonly growing near streams in well-drained grey to white sand. Flowering is swift following first heavy rains of the wet season in summer. In the tropics, plants die back rapidly as the season dries out and survive the 6-8 months of the dry season as dormant tubers.

Locally abundant.

Flowering period: October-January.

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