Coexisting Cytotypes ofArnica cordifolia: Morphological Differentiation and Local‐Scale Distribution

Abstract

Habitat differentiation is thought to play a role in polyploidy establishment and coexistence. Differences in morphology and microhabitat association could play a role in cytotype distribution, but random factors could also be important. Little work has been performed to examine mechanisms affecting local‐scale cytotype spatial distribution. Multiple cytotypes of Arnica cordifolia (Asteraceae) co‐occur in populations throughout Colorado. This study tests the hypothesis that habitat differentiation (specifically disturbance) controls the local distribution of triploids and tetraploids. We used flow cytometry to determine the local distribution of cytotypes in four populations. We measured plant morphological traits and environmental characteristics of each microlocation. We performed an experiment to test for differentiation in germination behavior between cytotypes. Tetraploids had higher germination success, were larger, and had a lower stomatal area index than did triploids. Both cytotypes were found in understory and roadside locations, with no relationship between cytotype prevalence and distance from the road. Triploid locations were not significantly different from tetraploid locations for a number of environmental factors. Triploids did not show a greater tendency to germinate preferentially in the light. Although triploids and tetraploids co‐occur in most populations of A. cordifolia, there is no evidence for consistent habitat partitioning at the local scale.