New Combinations in Megalastrum (Dryopteridaceae)

Abstract

One of Carl Christensen's many important contributions to fern taxonomy was demonstrating that Dryopteris, as defined around the turn of the century, was a vast, unrelated assemblage of ferns (Christensen, 1913, 1920). He indicated this diversity by dividing Dryopteris into 11 subgenera, using characters such as pinnule arrangement, hair type, and scale type that were not widely employed or appreciated by his predecessors and contemporaries. Ever since his work on Dryopteris, the trend has been to raise Christensen's subgenera to the generic rank or to treat them as subgenera in genera other than Dryopteris. In some cases, even his informal species groups have received generic status. This paper deals with one such grouping: the D. subincisa group of Dryopteris subg. Ctenitis. Nowadays, all pteridologists recognize Christensen's subgenus Ctenitis as a distinct genus, Ctenitis. Within Ctenitis s.l., one of Christensen's informal groups, comprising the species allied to Ctenitis protensa, was recently established as the genus Triplophylium by Holttum (1986a). He provided evidence that Triplophyllum is more closely allied to Tectaria than to Ctenitis. Another informal group, that of Dryopteris subincisa, was made a section of Ctenitis by Tindale (1965) and a genus by Holttum (1986b), as Megalastrum. We agree with Holttum that Megalastrum deserves generic status, as it is phenetically and cladistically distinct from Ctenitis. Furthermore, we are not aware of any species that is ambiguous with regard to placement in either Megalastrum or Ctenitis.