Ricinocarpos oliganthus is a species of flowering plant in the family Euphorbiaceae and is endemic to a small area in the south-west of Western Australia.

Ricinocarpos oliganthus is a monoecious shrub that typically grows to height of up to about 1.8 m (5 ft 11 in), its young branchlets more or less glabrous.

Flowering has been observed in June, and the fruit is an elliptic capsule 7.5–8.0 mm (0.30–0.31 in) long.

[2][3] Ricinocarpos oliganthus was first formally described in 2007 by David Halford and Rodney John Francis Henderson in the journal Austrobaileya from specimens collected near the Canna siding in 1996.

[2][3] Ricinocarpos oliganthus is listed as "Priority One" by the Western Australian Government Department of Biodiversity, Conservation and Attractions,[3] meaning that it is known from only one or a few locations that are potentially at risk.