Asplenium trichomanes ssp. trichomanes
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Basis for Listing
This small evergreen fern is wide-ranging, but it is often rare and isolated from other populations by long distances. The continental range map is consequently very general and includes considerable territory not actually occupied by this species. Only where suitable rocky habitat exists can Asplenium trichomanes ssp. trichomanes be found. In North America, there are population centers in the mountainous regions of the Appalachians north into the Ozarks and Canada, with sporadic occurrences elsewhere. Asplenium trichomanes ssp. trichomanes even occurs in Europe, Asia, Australia, and New Zealand. The species is composed of different races based on chromosome number, and while the plants look very similar, there appear to be differences in habitat preference.
The shape of the frond of A. trichomanes ssp. trichomanes is quite distinctive and is not likely to be confused with other ferns in Minnesota. The fronds are evergreen, elongate, and bear pinnate leaf segments (pinnae) that have roundish margins. The frond has a dark-colored, flexible rachis (stem). Spore-clusters arise from lateral veins on the underside of pinnae. The flap of tissue called the indusium opens toward the tip of the pinnae, and is angled toward the mid-rib (Tryon 1980).
In Minnesota, most populations of A. trichomanes ssp. trichomanes occur on moist, north to east-facing cliffs, particularly on ledges and in crevices. It also occurs in talus at the base of cliffs. Some of the cliffs are associated with large lakes that may provide a needed, climate-modifying effect. At least two populations are known to occur in association with open, exposed southeast facing cliffs where conditions are warmer, drier and sunnier. Populations in these more exposed habitats grow in sheltered crannies of cobbly talus. According to Moran (1982), the northern Minnesota populations belong to the diploid subspecies trichomanes, which apparently prefers noncalcareous rocks.
Biology / Life History
Asplenium trichomanes ssp. trichomanes is a perennial plant with evergreen leaves. Scaly rhizomes help anchor the plant in rocky habitats, but rhizomes do not function as reproductive organs. Reproduction is accomplished only through the germination of spores, although reproduction and recruitment rates are unknown. It is also not known how long individual plants live or how long a patch may persist. Individuals in patches or populations may number in the 10s to 100s; one site had over 1,000 plants. Patches tend to be separated from one another by long stretches of unsuitable habitat.
Conservation / Management
Asplenium trichomanes ssp. trichomanes is at risk because most of the populations in Minnesota are small and concentrated. This species is confronted with the same general threats as other rare cliff-dwelling plants in that suitable, mesic cliff habitats themselves are rare and limited, and that people are drawn to cliffs for their beauty and recreation. Also, A. trichomanes ssp. trichomanes is a particularly attractive, distinctive plant, which makes it especially vulnerable to wild plant collectors.
Conservation Efforts in Minnesota
Surveys of rare plant habitats have been conducted by the DNR Minnesota Biological Survey in portions of northeastern Minnesota, where cliff plant communities were targeted habitat. New populations are unlikely to be found except among the cliffs in the Border Lakes portion of Cook & northern Lake counties that remain to be surveyed. Based on available information, land managers have a sound basis for implementing protection strategies.
Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.
Moran, R. C. 1982. The Asplenium trichomanes complex in the United States and adjacent Canada. American Fern Journal 72:5-11.
Tryon, R. 1980. Ferns of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 165 pp.