A comparative study of clonal structure in two Sagittaria species with the same clonal growth modes: Sagittaria trifolia and S. pygmaea

Patterns of clonal growth in natural populations of two Sagittaria species (Sagittaria trifolia and Sagittaria pygmaea) were studied based on allozyme data, and spatial autocorrelation analysis was employed to assess their clonal structures. Ramets per multilocus genotypes in the studied populations varied from 1.556 to 5.468, and showed distinct features in clonal intensity between the two species. High clonal diversity was found in both species, with Simpson's diversity index ranging from 0.817 to 0.968 in the studied populations. Moran's I indices of multilocus genotypes in the studied populations, calculated by means of a Gabriel map, were higher than expected, which indicates that the spatial autocorrelation of clones was positive in each population. Comparatively, the value of Moran's I (I = 0.210∼0.354) for the S. pygmaea population was higher than that for the S. trifolia population. The change in Moran's I with different distance classes in each population revealed differences in the features of clonal dispersal in the two species: the ramets of each clone preferably distributed in a limited area in populations of S. pygmaea, whereas there was the potential for long-distance spread for the ramets of S. trifolia. The authors deduced that the spatial autocorrelation of multilocus genotypes should be directly related to the clonal growth modes of the species.