Botrychium oneidense (Gilbert) House
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Basis for Listing
Botrychium oneidense (blunt-lobed grapefern) has a very narrow geographic range compared to other Botrychium species and is known to reach the western limit of its range in Minnesota. It was first found in Minnesota in 1991, which sparked an intensive search to determine the full extent of its range and habitat preferences within the state. At the time it was designated as endangered in 1996, only a handful of populations had been found. Since that time, however, additional botanical surveys have been conducted, and more than 40 populations have now been located. Most of the populations are confined to moist depressions in mesic hardwood forests in the east-central part of the state, with a few populations recorded in mesic hardwood forests in extreme southeastern Minnesota. This new information indicates that this species is not as rare as previously thought, and endangered status is no longer necessary. However, because most of the populations are small and localized around small forest wetlands, they are vulnerable to certain forest management activities, particularly practices that create significant canopy openings. Hydrologic changes and invasive species may also pose a threat to the species and its habitat. Given these concerns, it is needed and reasonable to retain the species in threatened status.
Each individual B. oneidense plant produces a single leaf. In addition to the leaf, mature specimens produce a stalked, spore-bearing, reproductive structure. The spore-bearing structure may or may not be produced annually and can be three times as long as the leaf blade. The leaf diverges from the stem about 2.5-5 cm (1-2 in.) above the ground and may be up to 20 cm (8 in.) wide and 20 cm (8 in.) long. The blade is usually divided in a pinnate pattern 2 to 3 times. The ultimate leaf segments are mostly obtuse to rounded. Leaves stay bright green throughout the winter, with new leaves appearing in the spring (Gleason and Cronquist 1991; Wagner and Wagner 1993).
In Minnesota, B. oneidense occurs in mesic hardwood forests of Acer saccharum (sugar maple), Betula alleghaniensis (yellow birch), Fraxinus nigra (black ash), Quercus rubra (northern red oak), and Tilia americana (basswood). It occasionally occurs with Acer rubrum (red maple), Fraxinus pennsylvanica (green ash), Populus spp. (aspen), Pinus spp. (pine), Quercus macrocarpa (bur oak), and Thuja occidentalis (northern white cedar). Within the forest, B. oneidense usually grows in moist loam in low areas, swamp edges, or between the high and low water marks of vernal pools. It most often occurs as a few, scattered plants, however, as many as a hundred plants have been observed at one location. It often occurs with other Botrychium species, most commonly B. multifidum (leathery grapefern).
Biology / Life History
As a member of the Ophioglossaceae (evergreen grapefern family), the frond of B. oneidense is not killed by frost in the fall and holds its form through winter. During the summer, typically in late June, a new leaf begins to emerge and unfold. The overwintering leaf tends to disintegrate as the new leaf appears. An immature plant first emerges as a single, sterile leaf and develops a spore-bearing stalk in subsequent years. Therefore, many plants are sterile in any given year. Leaves in successive years become more dissected as the plant ages. In the past, B. oneidense has been treated as a form or variety of B. dissectum (dissected grapefern), or B. multifidum (leathery grapefern), as well as their hybrid. Botrychium dissectum, B. multifidum, and B. oneidense all look very similar when young (USFS 1999).
Conservation / Management
So far, B. oneidense has only been found in forested habitats in Minnesota. Most populations are small and localized around small, forest wetlands. These habitats are vulnerable to certain forest management activities. Forestry practices that create significant gaps in the canopy could alter the habitat by allowing more light and heat to reach the ground layer, which could change the composition of the community. Any significant damage to the forest floor such as soil compaction or rutting that might occur during a logging operation, could also threaten existing plants. Selective harvest of trees during winter, when the ground is frozen, would be a preferred forestry practice.
Botrychium oneidense is best identified by the shape of its single leaf, which is evergreen and survives for about 1 year. For this reason, B. oneidense can be reliably identified any time after the leaf is exposed after snow-melt in spring, and before the leaf is covered by leaf-fall in autumn.
Conservation Efforts in Minnesota
Several populations occur on state forest and county forest lands. Because these sites are typically managed for timber production, special attention must be given to protecting this species and its habitat.
Authorship / Revision
Author: Welby Smith, MN DNR, 2008. Revised: Welby Smith, MN DNR, 2016.