Osmunda angustifolia Ching ex Ching et Wang (Osmundaceae) was, formerly, known to be distributed in China (Guandong), Hainan, Hongkong, and Taiwan. Now, O. angustifolia is reported as a newly recorded species in Sumatra. A complete morphological description with photographs is presented. It is defined as a rare species in Indonesia. A cytological record is also reported for the first time for the Sumatran species. The somatic chromosome number of root tip cells of O. angustifolia is 2n = 44 (diploid).