(syn. Rhea Ϯ Lesser Rhea R. pennata) Gr. πτερον pteron feather; κνημη knēmē leg; "Mr. Gould brought before the notice of the meeting, from the collection of Mr. Darwin, a new species of Rhea from Patagonia ... the new species is distinguished from Rhea Americana of authors, in being one-fifth less in size, in having the bill shorter than the head, and the tarsi reticulated in front instead of scutellated, and in being plumed below the knee for several inches" (Gould 1837); "2460. b. PTEROCNEMIA, G. R. Gr. 9844. Darwinii, Gould, Voy. Beagle, pl. 47; G. R. Gr. & M. G. B. pl. 138; Pr. Z. S. 1860, fig. p. 209; Trans. Z. S. iv. pl. 70; Schl. De Dier. fig. p. 237. pennata, D'Orb." (G. Gray 1871); "Pterocnemia G. R. Gray, Hand List Bds. Brit. Mus., 3, 1871, p. 2. Type, by monotypy, Rhea darwinii Gould = Rhea pennata d'Orbigny." (Peters 1931, 1, 5). Var. Pterocnemis, Pterocnemys.