Genetic variation was analyzed in the endangered prairie forbPenstemon haydenii. Individuals from nine populations weresurveyed for chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA)variation. No cpDNA polymorphism was found. Analysis of mtDNA revealedvariation within and among populations. A minimum of eight haplotypeswere identified. The distribution of these genotypes suggests that thereis some correlation between geographic and genetic distances, whichreflects the minimal gene flow in thisspecies.