survey of allozymic variation among three members of the Sagittaria graminea complex (Alismataceae) from the southeastern United States

• Published in: The journal of the Torrey Botanical Society 1999-07, Vol.126 (3), p.181-187
• Main Authors: Hauber, D.P, Lege, L
• Format: Article
• Language: English
• Subjects: allozymes; Gels; Genetic distance; Genetic diversity; Genetic loci; Genetic variation; Genotypes; isozymes; Plants; Population genetics; Population mean; Sagittaria; Sagittaria graminea; Taxa; taxonomy
• ISSN: 1095-5674; 1940-0616
• DOI: 10.2307/2997273

The genetic relationships among three closely related taxa of the Sagittaria graminea complex from southern Mississippi, southeastern Louisiana, and the Florida panhandle were analyzed using isozymes. The present study investigates local populations of the three taxa, S. platyphylla, S. graminea var. graminea, and S. graminea var. chapmanii. In addition, three populations of S. lancifolia (not a member of the graminea complex) were included in the analysis. Over 400 individuals were analyzed from 15 populations using nine enzyme systems encoding 13 putative loci. All populations of S. platyphylla were uniform, sharing a single, multilocus genotype. Likewise, all but five of the 150 individuals sample from the S. g. graminea populations were isozymically identical. In contrast, the three populations of S. g. chapmanii were very diverse with a total proportion of polymorphic loci of 53.9%, a mean genetic identity of 0.784, and a mean GSTof 0.625. The within-population genetic diversities for S. g. chapmanii and S. lancifolia were determined to be moderate (HS= 0.115 and 0.086, respectively) after assessing that populations of both S. g. chapmanii and S. lancifolia displayed low levels of clonality. Genetic differentiation among the three taxa was substantial. The mean genetic identity between S. platyphylla and S. g. graminea was 0.538. The genetic identities between S. g. chapmanii and the other taxa, S. platyphylla and S. g. graminea, were 0.512 and 0.473, respectively. This degree of differentiation is somewhat surprising given the reported ease of crossability among these three taxa. The genetic identities between S. lancifolia and the other three taxa (0.485, 0.409, 0.521) are consistent with the current segregation of S. lancifolia from the S. graminea complex.