Allozyme variation and the taxonomy of Wolffiella

Abstract

Allozyme electrophoresis was carried out to estimate genetic diversity within and assess divergence between the 10 recognized species in three sections of the aquatic angiosperm genus Wolffiella. Eleven presumptive loci were used in the calculations. Highest variation was found in W. lingulata and W. oblonga, two common species with widespread distributions in North and South America. Four of the species showing low allozyme variation include W. caudata, W. denticulata, W. neotropica, and W. rotunda, all of which have restricted distributions. W. hyalina exhibits low allozyme diversity despite being widely distributed in Africa. Three species with intermediate levels of diversity include: W. welwitschii, which is widely distributed on two continents; W. gladiata, which occurs widely in North America; and W. repanda, which has a restricted distribution in Africa. Genetic identities between species of Wolffiella vary from 0.00 (no alleles in common) to over 0.94. W. lingulata and W. oblonga share the highest identity of any two species. These two species are viewed as most closely related and are difficult to distinguish in some instances. Species within the large sect. Wolffiella (incl. W. caudata, W. denticulata, W. gladiata, W. lingulata, W. neotropica and W. welwitschii) have identities ranging from 0.00 to 0.940, whereas identities with species in this section and the two species of sect. Stipitatae (incl. W. hyalina and W. repanda) are mostly 0.000, and the same applies for W. rotunda, the only species in sect. Rotundae. The two species of sect. Stipitatae, W. hyalina and W. repanda, have an identity of 0.800, which is higher than they share with any other species. Species of sect. Stipitatae have higher identities with W. rotunda (0.538, 0.504) than they do with any species of sect. Wolffiella, and W. rotunda is more closely related to sect. Stipitatae than to sect. Wolffiella. Allozyme data support the recognition of sect. Stipitatae as now constituted and provide evidence for the circumscription of sect. Wolffiella as presently recognized. However, W. denticulata is rather isolated within this section.