Diplazium pycnocarpon (Spreng.) Broun
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Basis for Listing
This woodland fern reaches the northwestern limit of its range in Minnesota, where it is confined to wooded bluffs in deep stream valleys of the southeastern corner of the state. Surveys have found Diplazium pycnocarpon absent from large areas of apparently suitable habitat. Most populations tend to be isolated from each other and in fragile habitats that are vulnerable to damage. Diplazium pycnocarpon was originally listed as a special concern species in Minnesota in 1984, but given its rarity and threats to its habitat, it was reclassified as threatened in 1996.
Diplazium pycnocarpon has creeping rhizomes (subterranean stems) with brown entire scales. The blade is oblong-lanceolate, 1-pinnate, with 20-30 pair of pinnae reduced in size toward the end of the blade. Pinnae are linear, nearly entire to shallowly crenulate, with 1-2 forked veins nearly reaching the sinuses. Sori are usually singular, elongate, and straight (Gleason and Cronquist 1991; Kato 1993).
Diplazium pycnocarpon occurs on north- and northeast-facing wooded bluffs, often near the base of the slope in rich organic loam near a creek, stream, or seepage spring. In maple-basswood forests, D. pycnocarpon is commonly associated with such notable ferns as Deparia acrostichoides (formerly Athyrium thelypterioides; silvery spleenwort), Dryopteris goldiana (Goldies's fern), and other rare plants. Although Diplazium pycnocarpon is a very rare species, and most populations consist of few individuals, some populations may comprise 100 or more individual plants.
Biology / Life History
Sterile fronds emerge in mid- to late May in Minnesota, later than many of the herbaceous species in its habitat. The plant sends up several fronds from the rhizome to form a clump. Fertile fronds are produced in mid-summer. These are often somewhat longer than the sterile fronds, standing up to 1 m (39.4 in.) or more in height. Diplazium pycnocarpon has been placed by some experts in the family Aspleniaceae (Gleason and Cronquist 1991; Kato 1993).
Conservation / Management
Diplazium pycnocarpon seems to be absent from large areas of apparently suitable habitat. Because it is distinctive and conspicuous, it is unlikely that surveys in occupied habitat would have failed to find it. Known occurrences are limited to fragile habitats in deep stream valleys in the Paleozoic Plateau or "driftless area." Diplazium pycnocarpon was probably not common even at the time of human settlement, and habitat changes since human settlement have likely reduced its populations. At the present time, the best way to preserve this rare species is to maintain and protect the forest habitat where it occurs. Special consideration should be given in forest management, as even selective logging could potentially alter the habitat if canopy openings increased light and temperature conditions on the forest floor. This would tend to dry and warm the soil, which could disrupt competitive relationships of plants and shift species composition. Any land uses employing heavy machinery may potentially damage the soil, especially on slopes. Livestock grazing could also degrade D. pycnocarpon habitats and directly injure plants.
Conservation Efforts in Minnesota
Several D. pycnocarpon populations occur in State Parks where they are protected from most threats. Other populations are in State Forests and Wildlife Management Areas, where resource management plans should incorporate habitat protection needs for this species.
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.
Kato, M. 1993. Diplazium. Pages 252-253 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York, New York.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.
Peck, J. H. 1982. Ferns and fern allies of the driftless area of Illinois, Iowa, Minnesota, and Wisconsin. Milwaukee Public Museum Press, Contributions in Biology and Geology Book 53, Milwaukee, Wisconsin. 140 pp.
Tryon, R. 1980. Ferns of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 165 pp.