Botrychium campestre var. lineare W.H. Wagner
Slender Prairie Moonwort
Basis for Listing
Botrychium campestre var. lineare (slender prairie moonwort) is a species with a very complicated history. Actually, it is the history of our understanding of this species that is complicated. There are herbarium specimens of this species dating back to at least 1902 (Barton and Crispin 2004). However, it was not recognized as a new species until 1994, when it was named B. campestre var. lineare (Wagner and Wagner 1994).
Botrychium campestre var. lineare is among the least frequently sighted of all moonwort species, which is probably a true reflection of its rarity (Farrar 2009). In July of 1999, a petition was initiated to list B. campestre var. lineare as a threatened species under the federal Endangered Species Act (Carlton 1999). The petition was based on the perceived rarity of the species, a historic decline, and demonstrable threats. As of 2015, B. campestre var. lineare had no federal status. Based on recent research, Farrar (2009) has recommended reclassifying B. campestre var. lineare as B. campestre var. lineare; though the significance of this change bears little on the conservation needs of this plant.
Botrychium campestre var. lineare was discovered in Minnesota in 2000 at a site near Trommald in Crow Wing County; eventually, about 20 plants were found at the site. It was found for a second time in 2006 at a site in St. Louis County, and for a third time in 2015 at a site in Marshall County. Estimating population size or trends for Botrychium is notoriously difficult. The individual plants are very small and difficult to find, even in a good year. In a bad year they may be nearly impossible to find. As a result, we know very little about these three populations. Given the extremely small number of known populations and the small size of those populations, Botrychium campestre var. lineare was listed as endangered in 2013.
The pinnae of B. campestre var. lineare have the narrowest pinna span of all moonworts, hence the common name, "slender moonwort". They broaden scarcely at all toward their outer margin, except as they divide, usually into 2 lobes diverging at an angle of about 45 degrees. Only two other species approach this morphology, both of them closely related to B. campestre var. lineare. Botrychium campestre (prairie moonwort) has broader pinnae that are less deeply lobed and a rachis that is broader relative to the total leaf width. Narrow-pinnae forms of B. ascendens (upswept moonwort) may be similarly lobed, but the lobes broaden toward an outer margin that is dentate. At maturity, the sporophore stalk of B. ascendens is usually greater than half the length of the trophophore, whereas it is less than half the length of the trophophore in B. campestre var. lineare (Farrar 2011),
On a global scale, most of the known populations of B. campestre var. lineare occur at high altitudes or northern latitudes in the western part of the continent (Farrar 2011). Most records are from non-acidic substrates in meadows and grassy roadsides.
In Minnesota, there are currently three known sites of B. campestre var. lineare. Two of the sites are in habitats created by iron ore mining. One of these is a tailings basin in Crow Wing County; the other is a mine “dump” in St. Louis County. Both sites have been abandoned for many decades, and, presumably, B. campestre var. lineare arrived during some early period of habitat recovery. The vegetation at these sites now consists of early successional species from the surrounding forests (Laurentian Mixed Forest Province).
The third site is a dry slope in a prairie in Marshall County. This site is along the prairie-forest border that runs in a broad band from northwestern to southeastern Minnesota (Tallgrass Aspen Parklands Province). The soil is coarse and gravelly material, which is apparently a remnant of an abandoned road bed.
There is no obvious explanation for the dissimilarity of the three known sites. However, a number of observations strongly suggest that species of Botrychium (moonworts) rely heavily, if not entirely, on their mycorrhizal partner for photosynthates, mineral nutrients, and water. With mycorrhizal fungi as an intermediary, Botrychium have greatly reduced, direct interaction with their environment (Farrar 2011). In this case, the habitat needs of the fungi may take priority over the needs of B. campestre var. lineare.
Biology / Life History
The niche of B. campestre var. lineare in community succession is unknown. In fact, this is true for all closely related species of Botrychium. They seem to become established early in the successional process but are apparently absent in latter stages of succession. The period of time during which habitats are suitable may range from one to several decades. There are examples in the literature of Botrychium populations persisting at a particular location for more than 50 years (Farrar 2011).
It has been proposed that apparent populations of Botrychium be considered metapopulations (Farrar 2011). This approach assumes that there are small, scattered and transient subpopulations that have limited interaction but are components of a larger population, identified by genetic composition. The potential size of metapopulations of Botrychium is dependent upon the frequency and distance of spore dispersal (Farrar 2011). If this is indeed the case with B. campestre var. lineare in Minnesota, then each of the three known “populations” would be short-lived subpopulations of a larger long-lived population. The role of these subpopulations would be to produce and release spores that could be the founders of new subpopulations in some new habitat.
Conservation / Management
Considering the early successional stage of the habitats occupied by B. campestre var. lineare, it seems reasonable to assume that freezing the successional process at a stage favorable to Botrychium would serve the conservation interests of this species. Setting aside the wisdom of this approach, the techniques to delay the successional process in such a way as to favor Botrychium populations have never been developed. Furthermore, such actions might not be needed, or even desirable. If the metapopulation theory of Botrychium populations is correct, then transient early-successional habitats are exactly what this species needs.
Best Time to Search
Available evidence indicates the annual above-ground activity of B. campestre var. lineare is primarily from the middle of May to the middle of June. This is the best time to search. In cool and moist summers, the period of growth may be extended to the end of June or the early part of July.
Welby R. Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Barton, D., and S. Crispin. 2004. Conservation status of Botrychium lineare (slender moonwort) in Montana. Report to the U. S. Fish and Wildlife Service. Montana Natural Heritage Program, Helena.
Carlton, J. 1999. A petition to list Botrychium lineare as threatened or endangered under the Endangered Species Act. Biodiversity Legal Foundation.
Farrar, D. R. 2009. Determination of the taxonomic relationship between Botrychium lineare and Botrychium campestre. A study conducted under Order No. 10181-5-M847 of the U.S. Fish and Wildlife Service.
Farrar, D. R. 2011. Systematics and taxonomy of the genus Botrychium. <http://www.public.iastate.edu/~herbarium/botrychium.html>. Accessed 19 November 2016.
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.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.
NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.
Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.
United States Fish and Wildlife Service (USFWS). 2000. Endangered and threatened wildlife and plants; 90-Day finding of a petition to add Botrychium lineare (Slender Moonwort) to the list of threatened and endangered species. Federal Register 65 FR 30048:30048-30050.
United States Fish and Wildlife Service (USFWS). 2007. Endangered and threatened wildlife and plants; review of native species that are candidates for listing as endangered or threatened; annual notice of findings on resubmitted petitions; annual description of progress on listing actions. Federal Register 72 FR 69033:69033-69106.
Wagner, W. H., Jr., and F. S. Wagner. 1994. Another widely disjunct, rare and local North American moonwort (Ophioglossaceae: Botrychium subg. Botrychium). American Fern Journal 84(1):5-10.