SPEER, WILLIAM D.1*, CHARLES R. WERTH2, ELIZABETH SHEFFIELD3, and PAUL G. WOLF1. 1Department of Biology, Utah State University, Logan UT 84322, USA; 2Texas Tech University, Lubbock, TX, 79409, USA; 3School of Biological Sciences, Manchester University, Oxford Road, Manchester M13 9PT, UK. - North American Pteridium: insights on population structure and systematic relationships from morphology, isozymes, and chloroplast DNA.
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