Rare Species Guide

  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 (maidenhair spleenwort) be found. In North America, there are population centers in the mountainous regions of the Appalachians and Ozarks and north into 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.

In Minnesota, A. trichomanes ssp. trichomanes was previously known from the northern Border Lakes area in Cook County based on collections from 1938 to 1984. Then, from 1992 to 2012 a few previously unknown occurrences were found on cliffs in Lake and Cook counties (Border Lakes and North Shore Highlands subsections). Most of the known occurrences are on National Forest, State Forest, or State Park lands, which serves to protect the sites from development. However, this species' fragile microhabitats and isolated populations make it vulnerable to local extirpation by unpredictable events. For these reasons, A. trichomanes ssp. trichomanes was listed as a threatened species in Minnesota in 1984.

There is one herbarium specimen of A. trichomanes ssp. trichomanes collected from a site in Goodhue County in 1895. The location written on the herbarium label is given as Vasa, without site details or accompanying habitat description. Repeated attempts to locate this species in the vicinity of Vasa (The Blufflands Subsection) have failed, and the status of that population is unknown. Southeastern Minnesota cliffs are comprised of Paleozoic limestone, dolomite, and sandstone bedrock. If there were populations of A. trichomanes ssp. trichomanes there in the past, they may have represented the calciphilic tetraploid race, which would be a very interesting find. Plants that occur on Precambrian igneous and metamorphic rocks in northern Minnesota and in Michigan's Keweenaw Peninsula are probably mostly of the diploid race (Moran 1982).

  Description

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).

  Habitat

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.

Some plant species that may be found in association with A. trichomanes ssp. trichomanes include other ferns (Woodsia spp., Cystopteris spp.), Acer spicatum (mountain maple), and smaller cliff-dwelling plants such as Micranthes virginiensis (early saxifrage).

  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, though 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 in specific microhabitats. 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.

  Best Time to Search

Because the leaves of Asplenium trichomanes ssp. trichomanes are evergreen, this species can be identified year round.

  Conservation Efforts in Minnesota

The baseline survey of rare plant habitats has been completed by the Minnesota Biological Survey, where cliff plant communities were a targeted habitat. New populations are unlikely to be found except among the cliffs in the Border Lakes portion of Cook and northern Lake counties. Based on available information, land managers have a sound basis for implementing protection strategies.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

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.

Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.

Tryon, R. 1980. Ferns of Minnesota. University of Minnesota Press, Minneapolis. 176 pp.