Botrychium rugulosum W.H. Wagner
St. Lawrence Grapefern
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Basis for Listing
Like several other species of Botrychium, our knowledge of Botrychium rugulosum is constantly evolving. This species appears to be very rare in Minnesota and apparently throughout its range, however, it is chronically confused with the common B. multifidum (leathery grapefern). In fact, most of the purported records of B. rugulosum submitted to the Minnesota DNR for confirmation turn out to be B. multifidum. In order to get a reasonably certain identification, a carefully preserved herbarium specimen must be made and examined by a specialist. Photographs are not adequate documentation. Complicating the issue is the uncertain taxonomic relationship between these two closely related species. The habitat requirements of B. rugulosum are still not thoroughly understood, but most of the known Minnesota locations are either in open pine forests or in moist, grassy areas within a pine or oak ecosystem. As with many other threatened species, habitat alteration is a primary and continuing threat to the perpetuation of this species in the state. Botrychium rugulosum was listed as a threatened species in Minnesota in 1996.
In habit, B. rugulosum resembles B. dissectum forma obliquum (cutleaf grapefern) and B. multifidum with which it commonly grows, but its leaf emerges from the ground in late May before the former and after the latter. Sterile deltoid leaf blades average 4-8 cm (1.6-3.1 in.) long, with the stalk more or less the same length (shorter in sun forms and longer in shade forms). Unlike the rounded lobes of the leaf of B. multifidum, the B. rugulosum leaf has angular lobes, mostly 2-5 mm (0.08- 0.2 in.) wide, with the edge of the leaf mostly coarsely and irregularly toothed. Botrychium rugulosum's teeth are dentate (wide-based, squarish, outward-pointing) as opposed to the serrate (narrow, sharp, forward pointing, saw-like) teeth of B. dissectum forma obliquum. The leaf of B. rugulosum may maintain its green color, while the leaf of B. dissectum can turn a drab, reddish color and then become bronze-colored in autumn.
Botrychium rugulosum grows in low, moist habitats in brushy or grassy areas and in open forest areas. It can be found growing in mossy areas in forests of Pinus banksiana (jack pine) or P. resinosa (red pine). Botrychium rugulosum also occurs in the transition zone between these habitats and adjacent habitats. In most locations, there may be only 1 or a few individuals occurring with relatively more common species of Botrychium, especially B. dissectum and B. multifidum, with which it is often confused.
Biology / Life History
The leaf of B. rugulosum is semi-evergreen and persists through the winter. When summer approaches, the old frond deteriorates as the new frond emerges (U.S. Forest Service 1999). The species epithet rugulosum refers to its tendency to become more or less wrinkled and convex (Wagner and Wagner 1993). Another common name for this species is ternate grape fern.
Conservation / Management
The preference of B. rugulosum for open habitats and openings within forests suggests that it may be adapted to exploit certain habitats in early successional communities. This could complicate management, because the natural dynamics of early successional and rapidly evolving communities are notoriously difficult to mimic with artificial means. These habitats normally rely on a complex interaction of events as varied as an insect outbreak, windstorm, fire, and erosion. Very few of the known habitats of B. rugulosum are large enough or wild enough to support such ecosystem processes. Immediate threats include development projects, habitat alteration, herbicide, and water level manipulation (U.S. Forest Service 1999).
Conservation Efforts in Minnesota
The design of a Minnesota DNR off-highway-vehicle park near the town of Gilbert was modified to preserve some B. rugulosum habitat.
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.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 307 pp.
U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Botrychium rugulosum. 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: Botrychium rugulosum. United States Forest Service, Region 9, Duluth, Minnesota.
Wagner, W. H., Jr., and F. S. Wagner. 1982. Botrychium rugulosum, (Ophioglossaceae), a newly recognized species of evergreen grapefern in the Great Lakes area of North America (Pteridophyta). Contributions from the University of Michigan Herbarium 15:315-324.
Wagner, W. H., Jr., and F. S. Wagner. 1993. Botrychium. Pages 86-101 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York.