Pteridium aquilinum (bracken) is widespread throughout North America, where it is represented by varieties latiusculum, pseudocaudatum, pubescens, and caudatum. The first two North American taxa have been the subjects of population genetic studies using isozymes and morphology. The isozyme evidence indicates conspecificity, and morphological evidence supports current varietal status. To date, no such similar studies have been conducted for either vars. pubescens or caudatum. A more recent global (chloroplast DNA) study of Pteridium indicates a much closer relationship among the North American taxa (excluding var. caudatum) than suggested by morphology. The results of the chloroplast DNA study indicate that pseudocaudatum and North American latiusculum share a chloroplast haplotype. Thus, the chloroplast DNA data are consistent with the isozyme results. One surprising result from chloroplast DNA analysis is that the western North American pubescens and the Hawaiian var. decompositum share a common chloroplast haplotype. This suggests a closer relationship of Hawaiian bracken with North American rather than Eurasian populations. A population genetic study, similar to that already done for eastern North American bracken, is needed for western North America, including populations from Hawaii.

Key words: bracken, cpDNA, isozymes, phylogeny, Pteridium, systematics