Lescuraea saxicola (Schimp. in B.S.G.) Milde
Lustrous Bow Moss
Lescuraea frigida, Pseudoleskea saxicola, Pseudoleskea frigida
Basis for Listing
In Minnesota, several well developed patches of Lescuraea saxicola (lustrous bow moss) were discovered at a single site in Cook County (North Shore Highlands) in 2001 (Janssens 2010). There were no previous regional records from states or provinces adjacent to Minnesota; however, Crum (2004) newly listed the species for the Upper Peninsula of Michigan (Copper Harbor, Keweenaw County). The species has a scattered northern-hemisphere distribution of montane affinity in mainly western North America, with disjunct populations in Labrador, Vermont, and the Gaspé of Québec (Crum and Anderson 1981). Because the Minnesota patches belong to only a single documented population, there is too little information available to detect a statewide population trend at this time. However, similar mesohabitats have been extensively searched in the region, and no additional populations have been found. Given the species’ extreme rarity and limited geographic range in the state, its restrictive habitat requirements, the vulnerability of populations to degradation or destruction, and concerns over a potential range-wide decline Lescuraea saxicola was listed as a threatened species in 2013.
Lescuraea saxicola is a member of the large mainly epiphytic family of the Leskeaceae. Many of its species are field look-alikes, but at least in Minnesota, this single member of Lescuraea (mostly a western genus) is easily differentiated from other Leskeaceae by the irregularly or somewhat pinnately branched and radiculose plants (from 2 cm [0.8 in.] in the Minnesota specimen to 5 cm [2 in.] long), with glossy curved branches (hence its common name, lustrous bow moss) and somewhat curved-secund leaves (up to 1.5 mm ]0.06 in.] long). These are appressed when dry, somewhat erect-spreading when wet but do not react as dramatically to wetting as those of some other species in the family (e.g. Lindbergia brachyptera [lindbergia moss]). The margins of the leaves are distinctly recurved up to the sharply acuminate apex, slightly serrate above, and their laminae somewhat bi-plicate. The costa is stout below and nearly percurrent. The branches and stems are covered with small foliose paraphyllia, another character state that distinguishes it from all other family members in Minnesota and, most helpfully, from its common look-alike Leskeella nervosa (leskeella). The small quadrate alar cells form a large oblong patch along the base of the leaf and margins; the medial leaf cells are elongated up to oblong-linear, with pitted walls but only very slightly prorulose, such that the glossy field aspect of a patch of L. saxicola is still quite diagnostic for differentiating the species from the other matte Leskeaceae. No sporophytes have been found within the Minnesota population. They were apparently unknown originally (Sharp 1934) but described in detail in Lawton (1971).
Lescuraea saxicola mostly occurs on non-calcareous rocks in mountains (Sharp 1934; Lawton 1971; Crum and Anderson 1981). In Minnesota, L. saxicola occurs on exposed rocks in a riverine black ash swamp along the narrow deep canyon of the Brule River. This mesohabitat has been typed as black ash – aspen – balsam poplar swamp (northeastern).
Biology / Life History
Colonist sensu stricto (During 1979; 1992). In the mesohabitat described above, individual patches are not expected to survive long on rocks as these will accumulate a thin layer of organic material, and other bryophyte species will then quickly out compete L. saxicola. However, in the dynamic environment of the wet riverine forest, additional microhabitat most likely becomes annually available after ice break-up and spring floods.
Conservation / Management
Lescuraea saxicola has a specific arctic-montane habitat, and its dependence on the maintenance of cool and moist conditions will likely make the species susceptible to local and global extinction from climate change. This disjunct subarctic-alpine species' viability in Minnesota could be in particular jeopardy from climate change given that sporophytes appear to be rare.
Best Time to Search
The best time to search for L. saxicola is from May through September or essentially anytime the ground is not covered by snow.
References and Additional Information
Crum, H. A. 2004. Mosses of the Great Lakes forest. Fourth edition. University of Michigan Herbarium, Ann Arbor. 592 pp.
Crum, H. A., and L. E. Anderson. 1981. Mosses of eastern North America. In two volumes. Columbia University Press, New York, Yew York. 1330 pp.
During, H. J. 1979. Life strategies of bryophytes; a preliminary review. Lindbergia 5(1)2-18.
During, H. J. 1992. Ecological classification of bryophytes and lichens. Pages 1-31 in Bates, J. W. , and A. M. Farmer. Bryophytes and lichens in a changing environment. Clarendon Press, Oxford, Wotton-under-Edge, Gloucesterchire, England.
Janssens, J. A. 2003. Bryophytes of the Northern Superior Uplands and the Superior National Forest: inventory, assessment, and recommendations for conservation. Report submitted to the Minnesota Department of Natural Resources and the Superior National Forest. 382. pp.
Janssens, J. A. 2005. Proposed candidates of endangered, threatened, and special concern species of bryophytes for Minnesota: update June 2005. Report to the Minnesota Department of Natural Resoucres, County Biological Survey, St. Paul. 18 pp.
Janssens, J. A. 2010. MS Access database on Minnesota brophytes. Lambda-Max Ecological Research, Minneapolis, Minnesota.
Lawton E. 1971. Moss flora of the Pacific Northwest. The Hattori Botanical Laboratory. Nichinan, Miyazaki, Japan. 363 pp.
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.
NatureServe. 2009. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. <http.//www.natureserve.org/explorer>. Accessed 10 June 2009.
Sharp, A. J. 1934. Pseudoleskea frigida. Page 190 in Grout, A. J. 1928-1934. Moss flora of North America north of Mexico. Volume III. Parts 1-4. Published by the Author.