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Tetrabaculum cacatua (M.A.Clem. & D.L.Jones) M.A.Clem. & D.L.Jones, Orchadian 13(11): 490 (2002).
Dendrobium cacatua M.A.Clem. & D.L.Jones, Austral. Orch. Res. 1: 48-49 (1989). Type: cult. ANBG, 1986, M.A. Clements 3715 ex Queensland, Mt. Lewis road, 12 miles from Mossman-Mt. Molloy road, 28 May 1972, J.W. Wrigley 199 (holo CANB; iso BRI, K).
Dendrobium tetragonum var. giganteum Leaney, Orchidol. Zeylanica 1: 73 (1934). Type: Northern part of Australia, Leaney s.n. (not found).
Dendrobium tetragonum var. giganteum P.A.Gilbert, Austral. Orchid Rev. 2(4): 19-20, 26 (Dec. 1937), nom. illeg.; 7(2): 36 (June 1942), p. p. Type: cult Sydney, 17 Oct. 1930, P.A. Gilbert ex near Cairns, [Anon] (not found).
Occurs in north-eastern Queensland from Mount Windsor Tableland to Eungella.
Altitude: 900-1200 m.
Epiphytic or lithophytic herb forming pendulous clumps. Pseudobulbs pendulous, 30-50 cm x 0.6-0.9 cm, narrow and wiry in basal half, becoming broader and quadrangled along length, narrowing at apex, greenish brown. Leaves 2-5, prostrate, apical, ovate, 5-9 cm x 1.5-2.5 cm, dark green, thin, leathery, apex acute. Inflorescence an axillary raceme, 10-35 mm long, from upper nodes of pseudobulb, filiform. Flowers 1-4, resupinate, porrect, 60-80 mm x 40-60 mm, greenish yellow to pale yellow, occasionally with a few small spots and blotches. Sepals narrowly triangular, tapered, apices filiform. Dorsal sepal erect, 30-70 mm x 3-5 mm. Lateral sepals not widely divergent, falcate near base, drooping, 30-70 mm x 6-8 mm, bases fused to column foot. Petals erect, linear to filiform, 22-25 mm x 1 mm. Labellum projected forwards, recurved, 11-15 mm x 6-10 mm, white, 3-lobed; lateral lobes erect; midlobe narrow, shortly hairy, pointed, with 3 low parallel ridges. Column 4-5 mm long. Column foot slightly curved, 8-10 mm long, at right-angles to column. Capsules pendulous, dehiscent.
Occurs in dense rainforests and rainforest margins where it grows on trees in shady sites beside streams.
Locally common.
Flowering period: July-September.
Until recently known as either Dendrobium tetragonum var. cactua or Dendrobium cactua.
