Tree spider orchids are unusual in having pendulous pseudobulbs that are thin and wiry near the base then expand into a fleshy, four-sided upper section before tapering at the tip.

The flowers range in colour from green to pale yellow, sometimes with red blotches and a labellum that ranges in colour from white, to yellowish with red, brown or purplish markings.

[2][3][4] Dendrobium tetragonum was first formally described in 1839 by Allan Cunningham from a specimen "hanging loosely from the stems of small trees in dry shaded woods, Moreton Bay".

The description was published in Edwards's Botanical Register edited by John Lindley.

Different forms of the species occur in different areas of coastal or near-coastal New South Wales and Queensland.