An Evaluation of Sceptridium dissectum (Ophioglossaceae) with ISSR Markers: Implications for Sceptridium Systematics
نویسندگان
چکیده
—Sceptridium dissectum, the most variable North American grapefern species, demonstrates variation in degree of blade dissection, blade color, pinnule shape, and pinnule margins. Historically, various morphologies have been included within S. dissectum. For example, Clausen’s monograph recognized five infraspecific taxa in S. dissectum, of which only the morphologies of variety dissectum and obliquum are currently retained. However, the taxonomic status of the two varieties has been debated. We used ISSR (Inter-Simple Sequence Repeat) markers to assess the genetic distinctness of S. dissectum var. dissectum and var. obliquum in 17 Ohio populations. Five ISSR primers generated 69 reproducible loci. In UPGMA analyses and AMOVA, S. dissectum var. dissectum individuals did not cluster separately from var. obliquum individuals, nor did individuals from the same population cluster together. ISSR markers revealed levels of population genetic structure in S. dissectum similar to levels detected by previous isozyme investigations. Our results concur with recent treatments of S. dissectum that do not formally recognize infraspecific taxa, and may bring into question current species circumscriptions in Sceptridium. We illustrate the use of ISSR markers for examining taxonomic boundaries in Sceptridium. Species of Sceptridium Lyon, the evergreen grapeferns, are common members of temperate and north temperate habitats, though the genus has a worldwide distribution (Wagner and Wagner, 1983). In North America, the center of species diversity lies east of the Mississippi River to the Atlantic Coast, and from the southern Gulf Coast to the northern coasts of the Great Lakes (Wagner and Wagner, 1993). Within this range, Wagner and Wagner (1993) recognized seven species, and it is not uncommon to find more than one species at a single site (Wagner, 1960a). Most Sceptridium species inhabit a variety of moderately disturbed habitats such as secondary-growth woods, old fields, and grassy slopes, although some species may occur in more undisturbed habitats (Clausen, 1938). Species of Sceptridium, like other members of Ophioglossaceae, generally produce one epigeal leaf per year, which is divided into a sterile trophophore and a fertile sporophore (Clausen, 1938). Unlike some members of the family (e.g., Botrychium s.s.; Wagner, 1990), Sceptridium species do not always produce a sporophore, and under stressful conditions may not produce a trophophore (Wagner, 1960b; Montgomery, 1990; Wagner and Wagner, 1993; Kelly, 1994). The leathery, photosynthetic trophophore persists through the winter, hence the moniker ‘‘evergreen’’ grapefern. Sceptridium species, as well 1 Current address: Department of Botany, Miami University, Oxford, OH 45056. American Fern Journal 93(1):1–19 (2003)
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