The flowers are arranged on the ends of the branches, usually in groups of 4 to 12 on a glabrous rachis 2–8 mm (0.079–0.315 in) long.

Flowering occurs from August to December, and the fruit is a hairy, oblong follicle 8–11 mm (0.31–0.43 in) long.

[3][4][5][6] Grevillea rosmarinifolia was first formally described in 1825 by Allan Cunningham, in Barron Field's book, Geographical Memoirs on New South Wales, from specimens collected on the banks of the Coxs River.

[9] In 2000, Robert Owen Makinson described two subspecies of G. rosmarinifolia, and the names are accepted by the Australian Plant Census: Rosemary grevillea is native to New South Wales and Victoria, but is naturalised in South Australia and the Australian Capital Territory.

The type form from the Coxs River is thought to be extinct in the field, but was rediscovered by Donald McGillivray growing outside the Royal Botanic Garden Edinburgh in 1969.