Ranunculus lyallii is a large buttercup that can reach 40 in (1 m) or more. The round leaves are deep green, leathery, shiny, with a diameter up to 16 in (40 cm). The white flowers are up to 3 in (8 cm) across; late spring to summer, depending on the altitude.
Ranunculus lyallii is found in shrubby areas, snow tussock herbfields, beside streams, and on cliffs, in high rainfall areas, South Island and Stewart Island, New Zealand. Grazing by deer, and other introduced animals, has limited it, in many places, to growing on cliffs.