Taxonomic status and relationships of bracken ferns (Pteridium: Dennstaedtiaceae) of Laurasian affinity in Central and North America

Detailed quantitative comparisons confirm and extend the discrimination of four major morphotypes amongst brackens of Laurasian affinity in Central and North America. These are recognized here at subspecies level as: Pteridium aquilinum sspp. feei, pubescens, latiusculum, and pseudocaudatum. Measurements of spore size indicate that sporophytes of P. aquilinum ssp. feei are diploid (2 n = 104), as are sspp. pubescens, latiusculum, and pseudocaudatum. Phenetic cluster analysis based on DNA fingerprinting by arbitrarily primed polymerase chain reaction groups these four subspecies as genomically more similar to each other than to any taxa from other geographical regions. The chloroplast haplotype of ssp. feei is the same as that of sspp. latiusculum, pseudocaudatum, and pubescens with respect to the absence of both of the short direct repeats in the rps4–trnS region (haplotype A), whereas the European ssp. aquilinum (haplotype B) has one of these repeats, and the Southern Hemisphere brackens P. arachnoideum and P. esculentum (haplotype C) have the other. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 1–17.