Assessment of Morphological Variation in Eriastrum densifolium (Polemoniaceae): Implications for Subspecific Delimitation and Conservation

Abstract

Intraspecific morphological variation was investigated in the perennial sub-shrub Eriastrum densifolium to assess whether the five currently recognized subspecies adequately reflect the pattern and range of variation expressed in the species, and to determine if the endangered E. densifolium subsp. sanctorum is morphologically distinct from other populations. Vegetative and floral variation were analyzed at the species and population level, employing herbarium specimens, field collections, and common garden plants. The results of the analyses indicate that morphological variation within the species is largely continuous. The only exception is a group of plants distinguished from the remainder of the species by a single character, corolla tube length. This group of individuals matches the circumscription of E. densifolium subsp. sanctorum. The other four recognized subspecies fail to form well defined morphological groups in all analyses. Patterns of morphological variation are not correlated with either genetic variation or geography. The overall pattern supports the recognition of only two subspecies in E. densifolium. One group represents a single morphologi- cally divergent population (E. densifolium subsp. sanctorum), and the other group the remainder of the species, containing multiple, less divergent populations.