Abstract
Athyrium haleakalae K.R. Wood & W.L. Wagner (Athyriaceae), a small lithophytic fern from East Maui, Hawaiian Islands, is described and illustrated. Notes on its distribution, ecology, and conservation status are also presented. The new species appears to be an obligate rheophyte, preferring sites of fast moving water along concave walls of streams and waterfalls. Athyrium haleakalae differs from the only other known Hawaiian Athyrium, Athyrium microphyllum (Sm.) Alston, in having rhizomes 1-3 cm long and lanceolate blades 1- to 2-pinnate-pinnatifid, 3-8(-11) × 1-3(-4) cm, as compared to Athyrium microphyllum having rhizomes (10-)15-30 cm long and ovate to ovate-triangular blades 3-pinnate-pinnatifid to 4-pinnate, 30-82 × 20-50 cm.