PLEISTOCENE REFUGIUM ENDEMICS EXHIBIT GREATER ALLOZYMIC DIVERSITY THAN WIDESPREAD CONGENERS IN THE GENUS POLYGONELLA (POLYGONACEAE)

Populations of each of the 11 species of the North American angiosperm genus Polygonella (Polygonaceae) were sampled for electrophoretically detectable allozyme diversity. In contrast to expectations based on similar surveys in many other vascular plant groups, the two most widespread species of Polygonella showed reduced within-population gene diversity with respect to their narrowly endemic congeners. One possible explanation is that high levels of selfing in the widespread species have led to reduced population-level diversity. An alternative explanation is that large-scale migration during Pleistocene glaciations removed much of the diversity of these more northerly distributed species, while the endemics, several of which inhabit known Pleistocene refugia, were able to maintain higher levels of diversity because of population stability during the glacial cycles. If the latter explanation is correct, an important implication for conservation is that, for many genera in eastern North America, the species richest in gene diversity may be those most in danger of extirpation in the next decade, namely those species endemic to Pleistocene refugia such as the Lake Wales Ridge.