Coprosma perpusillais a native mat-forming or prostrate subshrub with freely branching 30–40 cm long stems that root from their nodes.

The small lanceolate to ovate leaves are up to 7 mm long and up to 3.5 mm wide on short shoots. The specific epithet perpusilla comes from the Latin per (very) and pusillus (very small), referring to the growth habit. The unisexual, terminal, sessile flowers occur in summer on erect branchlets, and range in colour from greenish white to orange-yellow with red flecks. The fruit is an ovoid drupe 4–6 mm long and is yellow-orange to orange-red in colour. The plant occurs in New Zealand and in Australia and the sub-Antarctic islands of Macquarie, Campbell, the Auckland and the Antipodes. Its New Zealand range is Gisborne (Raukumara Range), Volcanic Plateau (central volcanoes, Maungaharuru Range, Kaimanawa Range), Taranaki (Mt Taranaki, Pouakai Range.), Southern North Island (Ruahine Range, Tararua Range), Western Nelson, Sounds–Marlborough (including Mt Stokes), Canterbury, Westland, Otago (Mt Maungatua, central and western ranges), Fiordland; Stewart Island. In New Zealand, its altitude range is on the North Island (760)900–1430 m and in the South Island 850–1850 m. It grows on tussock lands, damp herbfields and rocklands.