Asplenium unisorum, the singlesorus island spleenwort, is a species of fern endemic to the Hawaiian Islands. It only lives between in the Waiûanae Range on the island of Oûahu. It is classified as critically endangered, with a fragmented, actively shrinking mature population of around 1,150.
It grows tall, with a diameter. Leaf stalks branch off the main stem, which also features a few "small black scales". The stalks themselves are "black and shiny", around long. Branching off from the stalks, the fronds of the fern are tall by broad.