Sadleria cyatheoides, commonly known as amaumau fern or -ama-u, is a fern species in the family Blechnaceae, in the eupolypods II clade of the order Polypodiales, in the class Polypodiopsida. It is endemic to Hawaii and inhabits lava flows, open areas, and wet forests on all major islands up to an altitude of 1,676 m (5,499 ft). Reaching a height of 0.9-1.5 m (3.0-4.9 ft) and a trunk diameter of 7.5-10 cm (3.0-3.9 in), -ama-u resembles a small tree fern. K-lauea's Halema-uma-u Crater is named for this species. The young fronds are often tinged red to block harmful rays from the sun.