Rare Species Guide

  Synonyms

Polystichum braunii var. purshii

  Basis for Listing

The geographic range of Polystichum braunii (Braun’s holly fern) is quite limited, and it is generally considered to be rare or local wherever it occurs. It was first found in Minnesota in 1966, during a geological survey of Cook County (Greene and Engstrom 1975). By the time the species was designated endangered in Minnesota in 1984, it had been found at a second location, about 4 km (2.5 mi.) from the first site. In subsequent years, the number of known locations increased to a total of 12 and included sites in adjacent Lake County. The largest populations contain up to 150 plants; however, most colonies have just 5-30 individuals. More recent survey results indicated that P. braunii was not quite as rare as previously thought, and endangered status was no longer necessary. However, given the species’ restricted range in the state, its absence from apparently suitable habitats, and the vulnerability of the populations it still requires protective status. In 2013, its status was changed to threatened.

  Description

Polystichum braunii is a large fern, up to 1 m (39 in.) tall, similar in size to Athyrium filix-femina var. angustum (lady fern), with which it commonly grows. Its growth form is tufted, with as many as 12 or more fronds arising from a scaly rhizome. The upper side of each frond is dark green. Sterile and fertile fronds are similarly bipinnate and taper to the base and tip. Each frond has 20-40 pairs of pinnae (the primary division of the frond). Pinnules (the smallest division of the frond) are narrowly ovate to oblong and are slightly auricled at the upper side. They are also sharply serrate, with incurved bristle-tipped teeth and have slender chaff on the lower surface. Sori are arranged in 2 rows near the midrib. Indusia are circular, peltate, and often have erose margins. Stipes and rachises have numerous distinctive pale brown scales.

  Habitat

In Minnesota, P. braunii plants have been located on small ledges and cracks on the steep walls of river gorges, at the base of cliffs, on shaded talus, and in a cobbly and seepy drainage of lowland Fraxinus nigra (black ash) and Thuja occidentalis (northern white cedar) (wet forest). However, most of the populations occur along moist and often rocky draws and ephemeral rocky streams in mesic hardwood forests and mesic mixed forests  dominated by Acer saccharum (sugar maple) and Betula allegheniensis (yellow birch). Known sites are cool, moist, and shaded and all but one occur within 8.5 km (5.3 mi.) of Lake Superior (North Shore Highlands).

  Biology / Life History

Polystichum braunii fiddleheads begin to emerge in early to mid-May. Fronds are fully elongated by mid-June and stay erect and intact until late fall, when they are pressed to the ground by snow. Fronds are somewhat evergreen, overwintering beneath the snow, and are still present in May, when new growth begins. Young plants were present at most colonies in Lake County during inventories conducted from 1999-2002 by the Minnesota Biological Survey. Young plants accounted for 5%-25% of the population at these sites.

  Conservation / Management

Threats to the continued existence of this species in Minnesota include major reductions in tree canopy cover, water table manipulations, and alteration of intermittent drainages. In particular, significant reduction of the canopy would likely change the growing conditions by drying the soil and increasing light levels. Both of these changes could alter the competitive advantage of P. braunii and favor the growth of competing species.

  Best Time to Search

The best time to search for P. braunii is from May through September, or essentially anytime the ground is not covered by snow.

  Conservation Efforts in Minnesota

The Minnesota Biological Survey has completed surveys in the North Shore Highlands subsection, where most potential habitat occurs. Most of the known colonies of P. braunii occur within State Parks and State Waysides. However, there are currently no management plans that specifically address the needs of this species.

  References and Additional Information

Brzeskiewicz, M., and D. Fields. 2003. Conservation assessment for Braun's Holly Fern (Polystichum braunii). U.S. Forest Service, Eastern Region, Milwaukee, Wisconsin. . Accessed 28 June 2010.

Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis. 473 pp.

Greene, J. C., and D. R. Engstrom. 1975. A new locality for Braun's Holly Fern in Minnesota. American Fern Journal 65:61.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Minnesota Department of Natural Resources, Division of Ecological Resources. 2008. Rare species guide: an online encyclopedia of Minnesota's rare native plants and animals [Web Application]. Minnesota Department of Natural Resources, St. Paul, Minnesota. Accessed 1 July 2009.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.

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

U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Polystichum braunii. United States Forest Service, Region 9.

U.S. Forest Service. 2000. Population viability assessment in forest plan revision. Questions for plant population viability assessment panel: Polystichum braunii. United States Forest Service, Region 9, Duluth, Minnesota.

Wagner, D. H. 1993. Polystichum. Pages 290-299 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York, New York.