Marianthus tenuis is a species of flowering plant in the family Pittosporaceae and is endemic to the southwest of Western Australia.

It is a slender, twining shrub with clustered, narrowly elliptic leaves and white flowers tinged with mauve and with darker spots on three of the five petals.

[7] The name Marianthus tenuis is a replaced synonym of de Candolle's Billardiera parviflora, described in his 1824 Prodromus Systematis Naturalis Regni Vegetabilis.

[8][9] Marianthus tenuis grows in open coastal heath on limestone and in woodland on laterite south from the Darling Range in the Avon Wheatbelt, Jarrah Forest, Swan Coastal Plain and Warren bioregions of south-western Western Australia.

[2][3] This marianthus is listed as "not threatened" by the Government of Western Australia Department of Biodiversity, Conservation and Attractions.