BARKER, MICHAEL S.* and WARREN D. HAUK. Department of Biology, Denison University, Granville, OH 43023. - An evaluation of Sceptridium dissectum (Spreng.) Lyon and S. oneidense (Gilb.) House (Ophioglossaceae) using ISSR markers: implications for Sceptrdium species circumscriptions.
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