Genetic Structure of the Mecardonia acuminata (Plantaginaceae) Complex in the Southeastern USA

Mecardonia acuminata (Plantaginaceae) is found in the southeastern United States and has traditionally been divided into three varieties. A quantitative analysis of morphological data supported the division into the three varieties, although the ranges of the varieties found in that study were not the same as their traditional ranges. Here we use ISSR data to examine the relationships of 238 individuals from 23 locations throughout the range of M. acuminata. Although there is genetic structure that is congruent across different analyses, the groups recovered are not consistent with morphology or geography. The results indicate eastern-western distributions of the species with centers of diversity not only in the south but as far north as the Central Basin of the Interior Low Plateaus. The results further suggest ongoing diversification of lineages of M. acuminata, or the presence of widespread genes that govern the morphological traits that are traditionally used in delimitating the varieties.