Dendrobium tetragonum, commonly known as the tree spider orchid, is a variable species of epiphytic or lithophytic orchid endemic to eastern Australia. 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. There are only a few thin but leathery leaves at the end of the pseudobulbs and up to five flowers on relatively short flowering stems. To allow for the variations in the species there are five subspecies and a variety, some with a unique common name.

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