HABITAT DIFFERENCES OF THREE LIATRIS SPECIES AND THEIR HYBRID DERIVATIVES IN AN INTERBREEDING POPULATION

Abstract

The genus Liatris (Compositae) affords a favorable vehicle for an analysis of ecological and spatial isolation and their relationship to hybridization. Three biotically sympatric species, L. aspera, L. cylindracea, and L. spicata, were found within a northeastern Illinois sand prairie. Distribution of the three Liatris species was clearly related to a series of elevation, soil moisture, organic matter, exchangeable cation, and available phosphorus gradients. Liatris aspera occupied the upper slopes and ridge tops which were high in potassium and phosphorus content but low in moisture, organic matter, calcium, and magnesium levels. Liatris spicata occurred on the lower slopes and depressions with high soil moisture, organic matter, calcium, and magnesium levels but low potassium and phosphorus content. The third species, L. cylindracea, was restricted to the intermediate mid slopes. These distributional belts intergraded and created broad zones of overlap with opportunities for hybridization. The extent of hybridization was related to the spatial association of species and the availability of intermediate habitats. Hybrids had relatively narrow habitat preferences, and as such, few of the available spectrum of habitats along the elevational gradients were suitable for their establishment.