Bacopa rotundifolia (Michx.) Wettst.
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Basis for Listing
Bacopa rotundifolia is currently known from only a few locations in southwestern Minnesota. All of the sites are in areas where human land use practices are intensifying and coming into conflict with conservation of the species. Rock quarrying, cattle grazing, and herbicide application are the most prominent threats. It seems that even the best remaining sites are small and harbor only a few individuals, which complicates conservation efforts. Bacopa rotundifolia was listed as a special concern species in Minnesota in 1984, however, elevating its status to threatened is currently being considered.
Bacopa rotundifolia is a small aquatic or amphibious plant with roundish, opposite leaves that clasp the rather thickish stem. The leaves are 1-3.5 cm (0.4-1.4 in.) long and 0.7-2.5 cm (0.3-1.0 in.) wide. The flowers are white or bluish-white and develop on short, recurved pedicels in the axils of the leaves. The flowers are 6-10 mm (0.2-0.4 in.) long and have 4 stamens, 5 sepals, and 5 petals. The stems are 5-40 cm (2.0-15.7 in.) long, and when stranded on mud the stem may root at the nodes.
Bacopa rotundifolia is basically an aquatic species but it doesn't occur in large lakes or rivers. Instead, it is found primarily in small rainwater pools on bedrock outcrops, and occasionally along the margins of shallow ponds, in the prairie region of western Minnesota. Typically, the water depth in suitable habitats is greatest in the spring when there is more rainfall and still some snowmelt available to fill the pools. However, the water is rarely more than several inches deep and it typically evaporates by mid-June, leaving the sediments at the bottom of the pool moist or sometimes dry and cracked. The plants are generally able to persist for a couple more weeks after the pools dry up, and then completely disappear from view by July. On rare occasions, pools may refill in the fall with heavy rains and the plants will reappear for a brief time.
Biology / Life History
During the course of the growing season, the habitat of B. rotundifolia changes from aquatic to terrestrial. This transition would seem to be a problem for an aquatic species yet B. rotundifolia adapts easily. In fact, this change may be necessary to stimulate flowering, seed production, or seed germination. Many of the species' occurrences are in small, isolated rainwater pools in depressions in rock outcrops, often only a few feet across. How B. rotundifolia disperses from one habitat to another is not known.
Conservation / Management
It is possible that before settlers converted the prairies and prairie wetlands to agricultural production B. rotundifolia was more common and widespread than it is now. It is also possible that certain well-chosen examples of prairie wetlands that were drained or badly damaged by cattle grazing could be restored to something closely approximating their original physical and hydrologic condition. If this were to happen, we could see B. rotundifolia re-colonize those habitats, and perhaps even return from a long-buried seed bank. That would benefit a number of prairie wetland plants and animals and should be a high priority for conservation organizations and land management agencies. However, until that happens, protection of existing habitats is crucial. This involves protecting them from intentional or unintentional contact with herbicides and other agricultural chemicals, cattle grazing, and rock quarrying.
Conservation Efforts in Minnesota
At least three sites of B. rotundifolia are on publicly owned land where conservation measures should be possible. In addition, in 2007, the Renville and Redwood County Soil and Water Conservation Districts in association with state and federal agencies coordinated an initiative to compensate interested private landowners for permanently protecting the most ecologically intact rock outcrops and associated wetlands in those two counties. A total of 86 ha (212 ac.) were enrolled into perpetual conservation easements as a result of this initiative, and B. rotundifolia is one of the rock outcrop species most likely to benefit from the program. In 2009, the program was expanded to protect an additional 214 ha (530 ac.) within a five county area of the Upper Minnesota River valley. Conservation plans, which outline conservation practices such as removal of invasive species and livestock exclusion, are being developed for each of the easement sites. Habitat maintenance and improvement measures such as prescribed burning, fencing, rotational grazing, and/or seeding are also included in the plans.
Barrett, S. C. H., and J. L. Strother. 1978. Taxonomy and natural history of Bacopa (Scrophulariaceae) in California. Systematic Botany 3(4):408-419.
Dolan, R. W. 2004. Conservation assessment for Roundleaf Water-hyssop (Bacopa rotundifolia (Michx.) Wettst.). U.S. Forest Service, Eastern Region, Milwaukee, Wisconsin. 21 pp.
Harris, F. 2009. Rock pools on the prairie. Minnesota Conservation Volunteer 72(423):30-39.
Minnesota County Biological Survey. 2007. Native plant communities and rare species of the Minnesota River valley counties. Minnesota Department of Natural Resources, Division of Ecological Resources, St. Paul, Minnesota. 153 pp.