Ranunculus lyallii (Mountain buttercup, Mount Cook buttercup, or, although not a lily, Mount Cook lily), is a species of Ranunculus (buttercup), endemic to New Zealand, where it occurs in the South Island and on Stewart Island at altitudes of 700–1,500 m. The species was discovered by David Lyall, (1817–1895), a noted Scottish botanist and doctor. Contemporary botanist Sir Joseph Hooker, (1817–1911), noted in his Flora Antarctica: Notable sites for the species include Aoraki/Mount Cook National Park and in other alpine areas of including the area around Arthur's Pass.