Polyploid evolution and biogeography in Chelone (Scrophulariaceae): Morphological and isozyme evidence

Chelone is a genus of perennial herbs comprising three diploid species (C. cuthbertii, C. glabra, and C. lyonii) and a fourth species (C. obliqua) tha t occurs as tetraploid and hexaploid races. To assess patterns of isozyme a nd morphological variation, and to test hypotheses of hybridization and all opolyploidy, we analyzed variation among 16 isozyme loci from 61 population s and 16 morphological characters from 33 populations representing all taxa and ploidy levels. Based on morphological analyses using clustering (unwei ghted pair group method using an arithmetic average) and ordination (princi pal components analysis and canonical variance analysis) methods, we recogn ize three diploid species without infraspecific taxa. Polyploids in the C. obliqua complex were most similar morphologically to diploid populations of C. glabra and C. lyonii. Patterns of isozyme variation among polyploids, w hich included fixed heterozygosity and recombinant profiles of alleles pres ent in diploids, suggested polytopic origins of tetraploids and hexaploids. Our data indicate independent origins of polyploids in or near the souther n Blue Ridge, Interior Highlands and Plains, and Atlantic Coastal Plain reg ions from progenitors most similar to C. glabra and C. lyonii. Extant tetra ploids ware not implicated in evolution of hexaploids, and plants similar t o C. cuthbertii appeared unlikely as diploid progenitors for polyploids. We propose multiple differentiation and hybridization/polyploidization cycles in different geographic regions to explain the pattern of allopatry and in ferred polytopic origins among polyploids.