Abstract
The fern genus Dryopteris (Dryopteridaceae) in the isolated Atlantic Ocean islands, Ascension and St Helena isreviewed. Three species are known from these islands. Dryopteris ascensionis is endemic to and the only Dryopterisspecies known from Ascension Island. This species now appears to be extinct since has not been recorded since 1975,and was not found during repeated searches in the 1990s. Two Dryopteris species, D. cognata and D. napoleonis, areendemic to St. Helena and are rare on that island. Dryopteris napoleonis is lectotypified.
Highlights
Dryopteris Adanson (1763: 551) is a genus of about 225 species (Kramer et al 1990: 110) in the strict sense, but is recently enlarged by Zhang (2012) to include several small mostly Asian genera, increasing the total to ca 350 species
The chief centre of diversity for the genus is the Sino-Himalayan region and south-western China, with minor centres of divergence in south-eastern and eastern Asia, Oceania, Africa, Europe and the Americas (Roux 2012). Both Ascension Island and St Helena are oceanic islands positioned along the mid-Atlantic Ocean ridge and are of volcanic origin
Ascension is about 1 million years old compared to St Helena which formed about 14 million years ago (Ashmole & Ashmole 2000)
Summary
Dryopteris Adanson (1763: 551) is a genus of about 225 species (Kramer et al 1990: 110) in the strict sense, but is recently enlarged by Zhang (2012) to include several small mostly Asian genera, increasing the total to ca 350 species. It is one of the larger genera in Dryopteridaceae (Christenhusz et al 2011) and has a nearly worldwide distribution. Dryopteris is less common in the southern hemisphere and nearly absent from Australia and New Zealand.
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