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A study was conducted to describe allozyme diversity in Schwalbea americana, a hemiparasitic endangered perennial herb, using a sample of 13 populations at 15 presumptive loci. Genetic diversity was found to be low for the species, within populations and for polymorphic loci. No polymorphism was detected in seven populations. Three loci were polymorphic across the species' range but frequencies of uncommon alleles were low. These suggested that population extinctions, decreases in population sizes and habitat fragmentation may account for low genetic diversity.

Estimates of genetic diversity maintained by plant species and its distribution within and among populations allows plant geneticists to predict, in a general way, the evolutionary potential of species. Single-gene markers, particularly allozymes, have been used to measure the genetic diversity of species. In this paper, the plant allozyme literature was reviewed to compare levels of genetic variation maintained by crop and non-crop species. Crop species (plant species intentionally cultivated by humans) have more allozyme diversity as a whole than other seed plant species, although the mean genetic diversity partitioned within populations of crop species was similar to that of other plant species. Populations of crop species were more genetically heterogeneous, an observation that was probably due to the higher proportion of crops that reproduce by self fertilization. Dicotyledonous crops have much less genetic diversity than monocotyledonous crops at the species and the population level and exhibit more inter-population genetic differentiation. Annual and perennial crop species had similar levels of genetic diversity and partitioned genetic diversity in similar ways. Predominantly selfing crops had somewhat less genetic diversity than outcrossing or mixed-mating species. Selling crops exhibited more population-to-population variation in genetic diversity and allele frequency differences were much greater among their populations. High population-to-population variation in genetic diversity increases the importance of empirical data for the design of sampling protocols., Biologists define evolution as a change in the genetic composition of populations (Dobzhansky, 1970). Since the availability of genetic variation is a necessity for evolutionary change, a central question in [...]

Rugelia nudicaulis (Asteraceae) and Glyceria nubigena (Poaceae) were evaluated to determine the extent of genetic diversity using allozyme variation. The two plant species endemic to the Great Smoky Mountains are both candidates for federal protection. Poaceae did not display allozyme variation, while different levels of such variation were observed for Asterceae.

Genetic diversity and clonal structure in the endangered shrub, Ziziphus celata, were studied using allozyme analysis. Results indicate that the species is multiclonal and that as much as 25% of the 13 enzyme systems' putative loci were polymorphic. Further, Ziziphus does not undergo sexual reproduction in situ. Conservation of this species in the wild may entail provisions for genotypic diversity to promote sexual reproduction in this self-incompatible shrub.

The genetic diversity in 10 natural populations of Sarracenia leucophylla Raf., a pitcher plant restricted to the southeastern United States, is studied. The role of gene flow in the geographic distribution of genetic diversity within the species is described.

The allozyme diversity and genetic structure of the Macbridea alba, a herbaceous perennial mint, is described. Studies indicate that the perennial life habit of M. alba and long-distance pollination of bumblebees may help maintain the genetic diversity within the species.