Besseya bullii (Eat.) Rydb.
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Basis for Listing
It appears that Minnesota is the population center for this Midwestern endemic species, which is considered rare or threatened wherever it occurs. When Besseya bullii was placed on the state endangered species list in 1984, more than half of the historically known populations of the species in Minnesota were located in what is now the metropolitan area of Minneapolis-St. Paul and surrounding suburbs. At that time, only 5 of 21 previously documented sites were known to survive. However, the work of the Minnesota County Biological Survey in eastern counties since the late 1980s documented quite a few additional locations for this species. Despite these recent discoveries, B. bullii is at risk because its preferred habitat closely coincides with the preferred siting of housing developments. Without statutory protection, these newly documented populations on bluff prairies, dry open woods, and savannas in the metropolitan area could disappear. Besseya bullii was reclassified as threatened in 1996.
Besseya bullii is quite distinctive and bears no close resemblance to any other species encountered in Minnesota. It is characterized by a dense spike of sessile, yellowish flowers, each with two, long, exserted stamens. Basal leaves are large, pubescent, and heavily veined. Stems are unbranched, and their many small, alternate leaves partially clasp the stem. Plants flower in early spring but the spike and basal leaves remain visible throughout most of the summer.
Besseya bullii is primarily a species of oak savanna communities, though it also occurs in dry prairies and oak woodlands (including dry-mesic oak (maple) woodlands, dry-mesic oak-hickory woodlands, and dry-mesic pine-oak woodlands). The Minnesota populations are largely restricted to the bluffs and terraces of the St. Croix, Mississippi, and Minnesota river valleys, with many populations occurring in the greater Twin Cities area. Terraces of the Cannon River also support a number of populations. Plants show a preference for partial to open light and upper slopes. Some populations exhibit a preference for less xeric north-facing slopes in prairie habitats. Soils are most often sandy to gravelly, well-drained soil derived from alluvium or limestone bedrock.
Biology / Life History
Besseya bullii is a perennial herb. Flowers usually appear in May and the fruits dehisce by late June. This species appears to produce flowers in its second or third year. The first couple of years the plant produces only basal leaves. Flowering plants produce larger and more numerous basal leaves than nonflowering plants. Pollinators are unknown, but several species of Bombus (bumblebees) have been collected on a western relative. There may be as many as 17 to 93 capsules per inflorescence, with anywhere from 1 to 24 seeds per capsule. Seeds are small and flat. Wind appears to be a method of seed dispersal, although distance of dispersal is limited. Seeds appear to germinate best within a few months after maturation. Seeds that experienced dormancy had low germination rates, regardless of stratification or hormonal treatments (NatureServe 2008).
Conservation / Management
Besseya bullii has suffered a significant decline because of habitat loss. Threats to its habitat include gravel mining, limestone quarrying, landfills, residential and industrial development, and succession of oak savannas to forests in the absence of fire. Management techniques should be used to maintain or regain suitable habitat conditions. Active management does not appear to be as necessary at gravel prairie sites due to the xeric conditions and increased erosion. More intensive management may be required at savannas or wooded sites where species vigor is decreased. Management tools may include fire, which may be effective in reducing woody vegetation and encouraging flowering. However, careful timing of prescribed fires is critical. Fire should only be used in early spring before plants appear above ground, usually during late March or early April. Once the plants appear above ground, even 2.5-5.1 cm (1-2 in.), they can be severely damaged by fire. Besseya bullii occurs in isolated patches, which makes it conducive to protection from certain types development, if protection of existing populations is incorporated into the early planning stages of development.
Conservation Efforts in Minnesota
The Minnesota County Biological Survey has been completed within the likely range of this species in the state. Of the many locations documented for B. bullii over the past 25 years, some populations have been destroyed, but many still survive. A number of populations occur on protected public lands, including the River Terrace Prairie Scientific and Natural Area, Afton State Park, and Wild River State Park, among others.
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.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. <http://www.natureserve.org/explorer>. Accessed 3 June 2008.