Acianthus borealis D.L.Jones, Austral. Orch. Res. 2: 5-6, t., f. 3 (1991). Type: Queensland; Cook District; Moomin, Atherton Tableland, 17°22’S, 145°25’E, 1030m, 2 May 1988, L. Lawler 9 (holo CANB; iso BRI, CANB).
Occurs in north-east and central Queensland, more or less between the Mt Windsor Tableland and Blackdown Tableland.
Altitude: 400-800 m.
Terrestrial herb forming spreading colonies. Tubers 2, ovoid, fleshy. Leaf solitary, prostrate, basal, held above soil level, ovate to cordate, 1.5-4.5 cm x 1.5-3.5 cm, dark green above, reddish-purple below, margins often undulate, apex apiculate. Inflorescence a terminal raceme, erect, 50-250 mm tall, green or reddish, fleshy, slender, shortly pedicellate. Flowers 2-20, crowded, resupinate, porrect to slightly nodding, 8.5-10 mm x 5-7 mm, greenish pink, labellum green to reddish. Dorsal sepal obliquely erect, hooded, ovate, 9-10 mm x 3.5-4.5 mm, 3 veins prominent; osmophore terete, 2-3.5 mm long. Lateral sepals free, projecting forward below the labellum, parallel or crossed, linear, 8-9 mm x 1 mm; osmophore 2-3 mm long, filiform. Petals spreading, lanceolate, 4 mm x 1 mm, apex acuminate. Labellum porrect to obliquely deflexed, oblong-ovate, 5-6 mm x 2.5-3 mm, margins finely denticulate, purplish, apex acuminate. Column curved, 3 mm long, widest at base. Column foot absent. Capsules erect, ellipsoid, 12 mm x 2.5 mm, green with red ribs, dehiscent.
Forms dense clonal colonies on ranges and tablelands. It is most abundant on sheltered sites in open forests but can also be encountered on rainforest margins. The plants emerge towards the end of the wet season and die down in spring. The small purplish flowers resemble mosquitoes and are insect-pollinated. Each flower lasts 4-8 days.
Flowering period: March to May.
Previously included in Acianthus fornicatus.