The flowers are red and densely hairy except at the base, the pistil 16–20 mm (0.63–0.79 in) long.

Flowering occurs from September to December, and the fruit is a glabrous follicle 18–22 mm (0.71–0.87 in) long with several longitudinal ridges.

[2][3][4] Grevillea rhyolitica was first formally described in 1997 by Robert Owen Makinson in the journal Telopea from specimens collected in 1990 by David Albrecht.

[4][5] The specific epithet (rhyolitica) refers to the usual occurrence of this species on outcrops of rhyolite rock.

[4] In 2000, Makinson described two subspecies of G. rhyolitica in the Flora of Australia, and the names are accepted by the Australian Plant Census: Subspecies rhyolitica of Deua grevillea grows in moist gullies and in steep rocky ridges on rhyolite in montane areas west and south-west of Moruya[7][8] and subspecies semivestita grows forest in broken escarpment country north-west of Moruya in south-eastern New South Wales.