Phenotypic plasticity and genetic diversity elucidate rarity and vulnerability of an endangered riparian plant

Anthropogenic environmental change threatens many species and can be especially challenging for rare species given their potentially limited capacity for migration and adaptation relative to more common species. The ability to acclimate via phenotypic plasticity could provide an important path to persistence, especially for rare species. We investigated the responses of an endangered plant species endemic to a highly dynamic riparian habitat in southeastern Tennessee, USA, and its most widespread congener to environmental change to elucidate their current statuses and future vulnerability. Specifically, we compared the population- and species-level plasticity of rare Pityopsis ruthii and common P. graminifolia to contrasting light, temperature, and water conditions in a growth chamber experiment to evaluate their potential to acclimate to environmental change. Contrary to our expectations, P. ruthii had greater phenotypic plasticity than its common congener in response to both altered l...