Cytological and Chromatographic Evidence for Interspecific Hybridization in Petalostemon

Abstract

Chromatographic profiles of flavonoid extracts of P. purpureum and P. gattingeri are quite distinct, P. purpureum showing 12 species-specific compounds, and P. gattingeri showing 6 specific compounds. Chromatographic profiles of all putative hybrids except one exhibit compounds specific to each parental species. Three types of chromosomal abnormalities exist in putative hybrids which are not present in either parental species, but completely normal meiosis is reported in several hybrids. In a revision of the genus Petalostemon Michx., Wemple (1965) reported that interspecific hybridization is possible within taxonomic sections of this genus but not between species of different sections. He created fertile, artficial hybrids between Petalostemon gattingeri (Heller) Heller and P. purpureum (Vent.) Rydb., members of sect. Purpurei. In nature, these species are usually ecologically isolated. Petalostemon gattingeri is endemic to limestone glades in Tennessee and Alabama, and P. purpureum is a prairie species. In the central basin of middle Tennessee, Petalostemon gattingeri is widespread on limestone glades, while only a few individuals of P. purpureum have been found in the area. Naturally occurring populations of putative hybrids of these two species were observed by Breeden (1968) in Cedars of Lebanon State Park in Wilson County, Tennessee. In these populations, P. gattingeri was found along a roadside and on patches of open limestone. Petalostemon purpureum was found in adjacent areas which Breeden considered to be prairie relicts. He measured fourteen morphological characters of the two parental species and of putative hybrids and found that the hybrids were generally intermediate between the two parental species or within the range of variation of one of them. The present study was undertaken to supplement morphological data with chromotog