The taxonomic status and relationships of bracken ferns (Pteridium: Dennstaedtiaceae) from sub-Saharan Africa

Abstract

Two morphotypes of bracken fern in the genus Pteridium Gled. ex Scop. occur in sub-Saharan Africa. The more common and widespread of these is assigned in contemporary systematic treatments to the European subspecies, P. aquilinum (L.) Kuhn ssp. aquilinum. We show that this African form is separable morphometrically and genomically from the European subspecies, and reinstate its earlier name P. aquilinum ssp. capense (Thunb.) C.Chr. The second African bracken, with a more localized tropical distribution mainly in the drainage basins of the Congo and Zambezi River systems, is confirmed as P. aquilinum ssp. centrali-africanum Hieron. ex R.E. Fr. We reject suggestions that this taxon be treated as a full species. Phenetic cluster analysis based on use of Arbitrarily Primed Polymerase Chain Reaction (A-P PCR) and Inter Simple Sequence Repeat (ISSR) fingerprinting of the nuclear genome provides evidence that the two African brackens are more closely related to each other than to other taxa, and sister to a grouping of the European sspp. aquilinum and pinetorum. The two African subspecies share solely with ssp. aquilinum a distinctive chloroplast haplotype carrying a 5-base direct repeat in the rps4–trnS region, confirming the close phyletic relationship between sspp. aquilinum, capense and centrali-africanum. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 148, 311–321.