It is a subterranean herb that has a horizontal rhizome and a head of up to sixty small white flowers with a pink tinge, surrounded by relatively large, cream-coloured to pale pinkish cream bracts.

Rhizanthella johnstonii is a leafless, sympodial, subterranean herb with a horizontal rhizome 60–120 mm (2.4–4.7 in) below the soil surface with an erect peduncle up to 60 cm (24 in) long.

[2][3] Rhizanthella johnstonii was first formally described in 2018 by Kingsley Dixon and Maarten Christenhusz in the journal Phytotaxa from specimens collected near a tributary of the Oldfield River by Alex George in 1979.

[3][5] As with other orchids in the genus Rhizanthella, all parts of the life cycle of R. gardneri, including flowering, are subterranean.

[3] Rhizanthella johnstonii is listed as "Threatened Flora (Declared Rare Flora — Extant)" by the Department of Environment and Conservation (Western Australia)[5] and has been nominated for listing as "critically endangered" under the Australian Government Environment Protection and Biodiversity Conservation Act 1999.