Utricularia geminiscapa Benj.
Basis for Listing
Utricularia geminiscapa (hidden-fruit bladderwort) is a floating aquatic plant of bog pools and fens. It was first discovered in Minnesota at a remote location in Lake County in 2004. That discovery expanded the known range of the species a considerable distance westward. Presumably it escaped detection for so long because it is so very rare and looks similar to other bladderworts when in the water. Once alerted to its presence in Minnesota, aquatic botanists began looking for it over a wider area. Even after several years of extensive searches, only a small number of additional occurrences were documented (Laurentian Mixed Forest Province); hence, it was designated threatened in 2013.
The only adjacent state where U. geminiscapa is known to occur is Wisconsin, where it is considered rare.
Utricularia geminiscapa is an aquatic plant that floats suspended in the water column. It does not float on the surface, and it does not root in the substrate. The flowering scape is the only structure that normally appears above the water. The stems are usually 5-15 cm (2-6 in.) long and float beneath the water surface in a fine mass. The leaves are 1-2 cm (0.4-0.8 in.) long; they are often forked once at the base, then forked several more times, the segments becoming shorter and narrower toward the tip. The bladders are attached to the leaf segments and are less than 2 mm (0.08 in.) across. The flowers are of 2 types: fully opening (chasmogamous) that rise above the water and non-opening (cleistogamous) that remain submerged below the water. Fully opening flowers (rare) have yellow two-lipped petals; the lower lip is 6-8 mm (0.24-0.31 in.) long, and the upper lip is a little shorter. The spur (extended sac at base of petals) is more or less straight and is two-thirds as long as the lower lip and more or less projecting below it. Non-opening flowers (common) are borne singly on relatively short and thick stalks, 5-15 mm (0.2-0.6 in.) long. They lack petals and any noticeable color. The fruit is a 2-valved capsule containing many small seeds (Reznicek et al. 2011; Taylor 1989).
This species can be difficult to distinguish from a small specimen of U. macrorhiza (common bladderwort), which is common and occurs across Minnesota. The yellow, chasmogamous flowers that appear above the water are much smaller in U. geminiscapa than U. macrorhiza, but it is rare to find chasmogamous flowers on U. geminiscapa. When this is the case, look underwater along the stem for a short, stiff branch, with a single, spherical structure at the end. This is the cleistogamous flower, and its presence will confirm the specimen as U. geminiscapa.
All Minnesota records are from ponds or pools in natural settings, usually in rich fens, poor fens, or bogs. Suitable aquatic habitats are acidic and usually have a soft bottom of peat or other organic sediments. These habitats generally do not experience significant wave action, strong water currents, flooding, or desiccation. Larger and more aggressive plant species are generally absent, possibly because they would need a firmer substrate in which to anchor their roots and water higher in nutrients.
Utricularia geminiscapa is not likely to be found in lakes, marshes, or any water body lacking the buffering effects of permanent wetland vegetation.
Biology / Life History
Utricularia geminiscapa is free-floating, just beneath the surface of the water. It does not develop roots or any other structures that anchor the plant.
Stems, even fragments of stems, may continue to grow throughout the growing season but will die at the end of the season, when the days shorten and the water temperatures cool. Before they die, a turion will be produced at the growing tip of each stem. A turion is a segment of the stem, with tightly packed leaves. It will survive the winter and will begin growing the following year, which is why turions are sometimes called “winter buds”.
Like all members of the genus (commonly known as bladderworts) U. geminiscapa is at least nominally carnivorous. It has the capacity to trap tiny organisms, mostly larval insects that live in the water. They are captured in small bladders that develop on the leaf segments. The bladders open quickly when a tiny animal touches trigger hairs that surround the opening of the bladder. The bladder opens rapidly, sucking in the animal, and snaps shut again, all in a fraction of a second (Marmottant 2011;video). This ability to capture small animals is thought to be an adaptation to living in a nitrogen-poor environment.
Conservation / Management
By all indications, U. geminiscapa is dependent on a specific and potentially fragile habitat type. The habitat, small pools or ponds within bogs and fens, is invariably part of a much larger habitat complex involving not only the aquatic habitat but associated wetlands and uplands. Effective conservation requires that the entire complex be considered a single system. What happens in associated habitats can be expected to affect the aquatic habitat as well.
Best Time to Search
Chasmogamous flowers are helpful to confirm identification of specimens but are not required. Cleistogamous flowers are perhaps even more helpful for identification purposes and are much more likely to be present on a specimen (see description above). Cleistogamous flowers have been seen on Minnesota plants during the months of July, August, and September.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Fassett, N. C. 1957. A manual of aquatic plants. University of Wisconsin Press, Madison, Wisconsin. 405 pp.
Marmottant, P. 2011. The ultra-fast trap of an aquatic carnivorous plant. YouTube [web application]. <https://www.youtube.com/watch?v=Zb_SLZFsMyQ&t=63s>. Accessed 08 February 2017.
Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.
Reznicek, A. A., E. G. Voss, and B. S. Walters. 2011. Michigan Flora Online. University of Michigan. <http://www.michiganflora.net/species.aspx?id=1615>. Accessed 13 March 2013.
Taylor, P. 1989. The genus Utricularia: a taxonomic monograph. Kew Bulletin Additional Series XIV. Royal Botanic Gardens, Kew, London. 724 pp.