Botrychium rugulosum W.H. Wagner
St. Lawrence Grapefern
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Basis for Listing
Botrychium rugulosum (St. Lawrence grapefern) is a small fern that grows in low, moist habitats in brushy or grassy areas and in forest openings. It is easily confused with 2 other Botrychium species and consequently has often been misidentified. When designated a threatened species in 1996, it was known from less than 20 locations in northern Minnesota. Since that time, our understanding of the species’ habitat preferences has evolved, and nearly 50 additional populations have been discovered. Botrychium rugulosum is now known to be more widely distributed in Minnesota than was formerly believed, and threatened status is no longer necessary. However, given its vulnerability to habitat alteration and habitat succession, B. rugulosum was retained as a species of special concern in 2013.
Visually, B. rugulosum resembles B. dissectum (dissected grapefern) and B. multifidum (leathery grapefern), with which it commonly grows; however, its leaf emerges from the ground in late May, before the former, and after the latter. The sterile, deltoid-shaped leaf blade averages 4-8 cm (1.6-3.1 in.) long, with the petiole 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 leaf of B. rugulosum has angular lobes, mostly 2-5 mm (0.08- 0.20 in.) wide, with the edges coarsely and irregularly toothed. The marginal 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 turn bronze-colored in autumn.
Botrychium rugulosum grows in low, moist habitats in brushy or grassy areas and in open forested areas. It can be found growing in mossy areas in (fire depedent) 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 one or a few individuals occurring with relatively more common species of Botrychium, especially B. dissectum and B. multifidum, with which it is easily confused.
Biology / Life History
The leaf of B. rugulosum is semi-evergreen and persists through the winter. When summer approaches, the old leaf deteriorates, as the new leaf emerges (USFS 1999). The species epithet “rugulosum” refers to the 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 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 (USFS 2000).
The best time to search for B. rugulosum is from early spring, when snow melts and the plants are revealed, to late autumn, before snowfall can cover them. Be aware: Botrychium species may not emerge every year, especially during drought.
Conservation Efforts in Minnesota
The design of a Minnesota Department of Natural Resources’ off-highway-vehicle park near the town of Gilbert was modified to preserve some B. rugulosum habitat.
Author: Welby Smith, MN DNR, 2008
Revised: Welby Smith, MN DNR, 2016