Arthrochilus rosulatus D.L.Jones, Austral. Orch. Res. 2: 10-11, f. 10 (1991). Type: Queensland; Cook District; Double Barrel Pinch, Shipton’s Flat Road, ca 8 km from Big Forks Junction, south of Cooktown, 15°45’S, 148°15’E, 6 June 1990, L. Lawler 83 (holo CANB; iso BRI, CANB).
Occurs in far north-eastern Queensland from Bamaga to south of Cooktown.
Altitude: 20-150 m.
Terrestrial tuberous herb forming spreading colonies. Sterile plants a basal rosette of leaves only. Fertile plants an inflorescence with a rosette encircling base of inflorescence. Leaves 3-4, obliquely erect, forming a basal rosette; lamina elliptic to oblanceolate, 1-3.5 cm x 0.8-1.2 cm, bluish green, paler beneath, apex subacute. Infloresence a terminal raceme, erect, 70-150 mm long, slender, green; pedicels obliquely erect, 3 mm long. Flowers 2-15, non-resupinate, erect to porrect, 8-13 mm long, pale green with reddish to brownish labellum glands. Dorsal sepal free, decurved, widest near apex, embracing basal quarter of column, linear-ovate when flattened, 7.5-9 mm x 2 mm, margins conduplicate, apex obtuse with short dorsal ridge. Lateral sepals reflexed against the ovary, oblong to lanceolate, falcate, 5.5-6.5 mm x 2 mm, distal margins conduplicate. Petals reflexed agaist the ovary, linear, falcate, 5.5-6.5 mm x 1 mm, apex obtuse, distal margins conduplicate, apex obtuse. Labellum free, recurved, 5 mm x 0.8 mm, hinged to the underside of the column foot by a claw 0.1 mm long, base dark purple, 1.6 mm wide, becoming green along length, apex obtuse. Callus insectiform, proximally fused to lamina, 3.5 mm long; central area with crowded, shiny, clubbed calli 0.6-1.2 mm long, reddish to brownish; apex broadly emarginate, 1.5 mm wide, with shiny dark reddish or blackish glands. Column incurved in a semi-circle, 9 mm long, inner surface shortly pubescent, light green, with 2 pairs of column wings; proximal column wings projecting forwards, broadly triangular, 2.5 mm x 3 mm, translucent with few purple spots; distal wings smaller, linear to tapered, falcate, 2 mm x 0.4 mm, divergent above anther. Column foot 3 mm long, apex anvil-shaped. Capsules erect, obovoid, 9 mm x 3 mm, dehiscent.
Occurs in open forests and monsoonal rainforest thickets on well-drained sandy soils and laterite, where it forms spreading colonies. It is easily recognised from Arthrochilus species by its flower stem arising from the centre of the rosette. It has an unusually long flowering period which reaches well into the dry season.
Scattered and generally uncommon.
Flowering period: November-July.