About Dendrobium tetragonum A.Cunn.
Dendrobium tetragonum is an epiphytic or lithophytic herb that bears pendulous pseudobulbs 150–600 mm (6–20 in) long and 6–9 mm (0.2–0.4 in) wide. Its pseudobulbs have a thin, wiry base, expanding into a fleshy, four-sided upper section with a tapering tip, and grow between two and five thin, leathery leaves. The leaves measure 50–90 mm (2–4 in) long and 15–40 mm (0.6–2 in) wide. Flowering stems are 10–35 mm (0.4–1 in) long, and hold up to eight flowers each. The number, size, and colour of the flowers vary by subspecies. Flowers range from 30 to 120 mm (1.2 to 4.7 in) long and 20 to 80 mm (0.79 to 3.1 in) wide, with colour varying from green to pale yellow, sometimes with red blotches. The labellum ranges in colour from white to yellowish, with red, brown, or purplish markings. Sepals range from 20 to 70 mm (0.79 to 2.8 in) long and 2 to 5 mm (0.08 to 0.2 in) wide, while petals range from 10 to 40 mm (0.39 to 1.6 in) long and 1 to 2 mm (0.04 to 0.08 in) wide. The labellum itself measures 8 to 15 mm (0.31 to 0.59 in) long and 6 to 20 mm (0.24 to 0.79 in) wide. Flowering occurs between April and November. Commonly called tree spider orchid, this species is usually epiphytic, growing on trees in rainforest or shady areas beside streams. It also sometimes grows on paperbark trees, especially Melaleuca styphelioides, and occasionally grows on rocks. Different infraspecific forms of the species grow in different coastal or near-coastal areas of New South Wales and Queensland. Dendrobium tetragonum var. cacatua occurs from the Mount Windsor Tableland near Cape Tribulation to Eungella National Park in Queensland. Subspecies cataractarum is restricted to the Connors Range, west of Cape Palmerston National Park in central eastern Queensland. Dendrobium tetragonum subsp. giganteum grows between the Iron Range and Mackay in Queensland. Dendrobium tetragonum subsp. melaleucaphilum is found from Blackdown Tableland National Park in Queensland to the Blue Mountains in New South Wales. Dendrobium tetragonum subsp. serpentis is restricted to the northern parts of the Blackdown Tableland. Dendrobium tetragonum subsp. tetragonum ranges from Fraser Island in Queensland to Tomerong in New South Wales.
