Assessing Morphological Species and Interspecific Relationships in North American Grapeferns (Sceptridium; Ophioglossaceae) Using ISSR Markers

Abstract Relationships among North American Sceptridium (sensu Škoda) species are often difficult to assess because of few stable distinguishing characters and high intraspecific variability. We used ISSR-PCR to examine relationships among four samples of Holubiella, 24 samples representing four diploid North American Sceptridium species, and a Russian Sceptridium sample. Nine ISSR primers yielded 147 polymorphic loci. We generated three neighbor-joining dendrograms using a Jaccard, Nei & Li, or Dice coefficient. All three coefficients cluster based solely on the presence of bands and not the absence. ISSR data analyses across all three coefficients were consistent with published analyses of DNA sequence data in supporting Holubiella as sister to all Sceptridium species sampled. Sister group relationships among the four Sceptridium species were not consistent across all three neighbor-joining analyses, and bootstrap support was generally low. However, 26 of the 29 samples consistently clustered with other samples of similar morphology, and these clusters generally supported current species concepts. In taxa such as Sceptridium, with low DNA sequence variability among species, ISSR-PCR may provide an important tool for evaluating morphologically defined species, but additional data are necessary for establishing robust hypotheses of phylogenetic relationships.