Synonyms

Fimbristylis interior

  Basis for Listing

Fimbristylis puberula var. interior (hairy fimbry) is a plant of the southern Great Plains and southeastern U.S. It is known to have occurred at only two places in Minnesota, both are calcareous fens. One site is in Redwood County (Minnesota River Prairie Subsection) and was confirmed as recently as 2017. The second site is in Wilkin County (Red River Prairie Subsection) and has not been seen since its initial discovery in 1987. Recent visits to the site concluded that the habitat has suffered severe degradation and failed to locate any F. puberula var. interior. That population is now feared extirpated.

Calcareous fens are small, often less than 0.4 ha (1 acre), groundwater-fed wetlands that are rich in calcium and magnesium bicarbonates and low in dissolved oxygen. They are also very fragile and extremely vulnerable to changes in groundwater levels. There are over 100 calcareous fens known to occur in Minnesota, but only one fen is known to currently harbor this rare species. For this reason, F. puberula var. interior was listed as an endangered species in 1996.

  Description

For clarification, there are two varieties of this species; only var. interior occurs in Minnesota. The other variety is var. puberula, which occurs to the south of Minnesota. Fimbristylis puberula var. interior is a slender spare-looking plant with a loose cluster of small dull brown spikelets at the top of each stem. The stems tend to occur singly or a few together, rather than in dense clumps. The leaves and bracts are rather short and decidedly slender--they are not likely to be noticed in the field. In Minnesota, there are only two species of Fimbristylis, and they should not be confused with each other. Fimbristylis puberula var. interior is a larger plant than F. autumnalis (autumn fimbry) in all regards. The height of the plant is greater, the spikelets and scales are larger, and they occur in different habitats.  

Technical description: Plants perennial. Culms arising singly or few together, angular or compressed in cross-section, erect or ascending, with hard swollen bases, 10--75 cm long. Rhizomes scaly, orangish, to about 3 cm long. Leaves essentially basal; blades involute or channeled, not exceeding the culms in length, 0.5--1.5 cm wide. Inflorescence terminal, simple or compound, 2--6 cm long; subtended by 1--5 leaf-like bracts, the longest of which may or may not exceed the inflorescence. Spikelets 2--20 in number, 5--15 mm long, each consisting of 12--40 flowers; typically the central spikelet sessile and the lateral spikelets on ascending or spreading peduncles. Flowers bisexual; perianth absent. Floral scales glabrous, concealing the achenes, brown with green midrib; midrib excurrent as an apiculus. Achenes about 1 mm long, biconvex, yellowish to brown, with numerous vertical columns of small pits; tubercle absent. Maturing mid-July to late August (Smith 2018).

  Habitat

The two populations known to have occurred in Minnesota were found in calcareous fens. Fens are saturated, peat-filled wetlands sustained by upwelling groundwater. They are open (non-forested) habitats dominated by sedges (primarily species in the genus Carex). Associated species of F. puberula var. interior include other rare sedges such as Scleria verticillata (whorled nutrush) and Rhynchospora capillacea (hair-like beak rush), and the more common Lobelia kalmii (Kalm's lobelia) and Triglochin palustris (marsh arrowgrass).

  Biology / Life History

Fimbristylis puberula var. interior is a perennial species that flowers from July to mid-August. Flowers are wind-pollinated. The seeds (achenes) possess no specialized mechanism for dispersal and probably rely on gravity and perhaps water currents for short-range dispersal. The mechanism for long-range dispersal is not known but likely happens as a result of incidental movement by birds that might forage in the habitat. Established populations maintain their presence by the perennial nature of the rhizome, which is a short underground stem that survives winter in a dormant state and produces new stems and roots in the spring/summer.

  Conservation / Management

Both of the calcareous fens where F. puberula var. interior have been found are on private land and have experienced some level of degradation because of incompatible land use practices. Of paramount importance is the maintenance of the natural hydrological regime that sustains the fens. It needs to be remembered that calcareous fens are permanent wetlands where water levels fluctuate very little during the course of a growing season, even during times of drought. Fen vegetation will be seriously, and probably irrevocably, damaged if “dewatered” for even a short period of time. It is also important to exclude livestock and prevent surface erosion and sedimentation. Periodic dormant season fire may be helpful in controlling encroaching shrubs but must be timed carefully to avoid damaging F. puberula var. interior.

  Best Time to Search

The best time to search for Fimbristylis puberula var. interior is while it is in flower or fruit, from July to October.

  Conservation Efforts in Minnesota

Although the Minnesota Wetland Conservation Act currently provides special protection for calcareous fens, the very limited number of occupied sites makes F. puberula var. interior vulnerable to extirpation from random or catastrophic events. The DNR's Minnesota Biological Survey has searched for rare biological features in the two counties where this species is known to occur. Because additional populations have not yet been discovered, the ecological significance of these two sites is elevated and they warrant special protection.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Kral, R. 2002. Fimbristylis. Pages 121-131 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.