Species of Sceptridium (grapeferns) are found throughout most of North America, with a continental center of diversity in the Eastern United States. The combination of few stable species-specific characters and substantial infraspecific morphological variation makes Sceptridium species difficult to distinguish. Sceptridium dissectum (Spreng.) Lyon, the most variable North American grapefern species, demonstrates variation in degree of blade dissection, pinnule shape, pinnule margins, and blade color. In 1938, Clausen recognized four varieties and one subspecies within S. dissectum. Of Clausen’s five infraspecific taxa, only var. obliquum (Muhl.) Clute and var. dissectum Spreng. are currently retained. In 1960, Wagner raised S. dissectum var. oneidense (Gilb.) Farwell to species status citing differences in leaf color, periodicity, and root morphology. Because our observations revealed no clear morphological discontinuities among taxonomic units in Sceptridium, we examined the relationships among S. oneidense, S. dissectum var. dissectum, and S. dissectum var. obliquum using molecular markers. Preliminary collections from 17 Ohio populations included a total of 69 sporophytes: 10 S. dissectum var. dissectum, 52 S. dissectum var. obliquum, and seven S. oneidense individuals. We used ISSR (Inter-Simple Sequence Repeat) markers to assess the genetic distinctness of S. oneidense, S. dissectum var. dissectum, and S. dissectum var. obliquum. Five ISSR primers generated 69 reproducible loci. In UPGMA and AMOVA analyses, individuals identified as S. oneidense did not cluster with other individuals assigned to the same species. Likewise, S. dissectum var. dissectum individuals did not cluster together. Thus, our results demonstrated that the morphological features of S. oneidense, S. dissectum var. dissectum, and S. dissectum var. obliquum did not correlate with ISSR banding patterns. We question recognizing S. oneidense as a distinct species, and the evolutionary relevance of retaining infraspecific taxa in S. dissectum.

Key words: grapeferns, ISSR PCR, Ophioglossaceae, Sceptridium, species delimitations