Genetic variation in two Chamaecrista species (Leguminosae), one endangered and narrowly distributed and another widespread in the Serra do Espinhago, Brazil

The Serra do Espinhaqo in Brazil is under continuous and increasing levels of human disturbance. It has a large number of endemic plant species such as Chamaecrista semaphora (Irwin and Barneby), an endangered species with extremely narrow range. We studied the genetic diversity of C. semaphora and compared it with Chamaecrista mucronata (Spreng.) Irwin and Barneby, a widespread congeneric species distributed over the entire Serra do Espinhaqo, in an attempt to provide information for conservation strategies. Two populations of C. mucronata and the only two known populations of C. semaphora from Serra do Cipo were screened for variability using random amplified polymorphic DNA (RAPD) markers. Populations of C. semaphora exhibited a lower percentage of polymorphic markers (16.9%) and Shannon's Diversity Index (H'(pop) = 0.124) than C. mucronata populations (43.3% and H'(pop) = 0.299). Most of the genetic variability of both species studied was distributed within populations; C. semaphora populations (Phi(ST) = 0.198) were less divergent than C. mucronata populations (Phi(ST) = 0.378). The risk of extinction for C semaphora is large owing to its low level of genetic diversity compared with its widespread congener and because of increasing habitat destruction. Both populations of C. semaphora urgently need protection to maximize the genetic diversity of this species and diminish further substantial loss within the populations.