Assessing habitat requirements and genetic status of a rare ephemeral wetland plant species, Isoëtes butleri Engelm

Isoëtes butleri Engelm. (Butler's Quillwort) is a lycopod endemic to the central and southeastern United States. It inhabits sparsely vegetated moist depressions within dolomite prairies that become ephemeral wetlands in the spring. Classified as endangered in portions of its range (Illinois and Kentucky), little is known about the ecology and genetics of I. butleri. In Illinois, the five known populations are disjunct from all other known populations, and there is concern that these populations could be vulnerable to a number of threats, including a lack of suitable microhabitats, displacement by other plant species, accumulation of plant litter, and low genetic diversity and limited gene flow. We evaluated these putative threats by analyzing demographic data collected by Plants of Concern, a citizen-science rare-plant monitoring program; performing experimental litter removals; and assessing population genetic structure. There were no significant differences in soil nutrient availability in topographically similar depressions with and without I. butleri; however, areas inhabited by I. butleri had lower abundance of woody species and higher abundance of conservative (habitat specialist) species than uninhabited areas. Following experimental litter removal, I. butleri exhibited lower size but higher density and recruitment. We found that all populations had high genetic diversity. However, there was also evidence of high inbreeding, which may be due to spatially fine-scale genetic structure and poor dispersal ability. Our findings suggest that reductions of woody plant growth and accumulated litter—both of which can be achieved through prescribed fire—should be management priorities for I. butleri conservation.