NATURAL INTERSPECIFIC HYBRIDIZATION IN EASTERN NORTH AMERICAN CLAYTONIA

The eastern North American spring ephemeral Claytonia virginica (Portulacaceae) is well known for its great variation in chromosome number. The origin and significance of this cytological diversity has been a source of some controversy over the last two decades; in particular it has been suggested that one major source of variation could have arisen by allopolyploidy following hybridization between C. virginica and the second eastern North American representative of the genus, C. caroliniana. However, there has been no rigorous demonstration of natural hybridization between these taxa, and attempts to document hybridity have been hampered by a paucity of distinguishing morphological characters. Nuclear ribosomal gene markers are, however, able to distinguish between the two species and provide a means of identifying hybrid plants. We have found a locality in central New York state where the two species cooccur; in this population, hybrid individuals with additive ribosomal gene patterns are found in a zone of overlap between the two parental species. These hybrids are morphologically intermediate and have reduced pollen stainabilities, and appear to be F₁ individuals.