Botrychium spathulatum W.H. Wagner
Basis for Listing
Botrychium spathulatum (spatulate moonwort) is a small terrestrial fern, with a widespread yet limited distribution; populations can be found in scattered localities the whole length of the Rocky Mountains and across the northern Great Lakes region. It was not known to occur in Minnesota until 1998, when two populations were found, one near Trommald in Crow Wing County and the other in the Superior National Forest in Cook County (Laurentian Mixed Forest Province). Intensive searches since that time have failed to turn up more than a small handful of additional occurrences in this region. In 2015, another small handful of populations was discovered about 320 km (200 mi.) away, near Gatzke in Marshall County (Tallgrass Aspen Parklands Province). There is still much uncertainty about the status of this species, since it was not formally described until 1990 (Wagner and Wagner 1990). Given the extreme paucity of populations despite targeted botanical surveys, the small size of those populations, the vulnerability of the populations to habitat succession, and the potential need for active management to maintain habitat conditions, Botrychium spathulatum was designated endangered in 2013.
Members of the genus Botrychium (moonworts) have a peculiar morphology, which is quite unlike most other ferns. They typically have only one leaf per year, which is produced by an underground stem. The above-ground portion of the leaf is divided into two parts. One part, the "expanded" part (called the "trophophore"), is usually photosynthetic and sterile. The other part bears numerous globose sporangia and is called the "sporophore" or "fertile segment". The trophophore and sporophore are joined into a common stalk or petiole. The common stalk extends underground to the apex of the stem, where its base encloses the apical bud.
Botrychium spathulatum can be differentiated from the similar B. minganense (Mingan moonwort) as well as B. gallicomontanum (Frenchman’s Bluff moonwort) and B. pallidum (pale moonwort) by its sessile trophophore, with the basal pinnae being the largest, and pinnae margins that are rounded and entire or, if dissected, irregularly so, with segment margins rounded and entire. It most closely resembles B. ascendens (slender moonwort), which may occur at the same site. However, in B. ascendens, the outer pinna margin is coarsely toothed and, if divided into segments, pinnae of B. ascendens are symmetrically cleft into 2 or 4 spreading lobes, with toothed outer margins (Farrar 2011).
As is the case with all species of Botrychium, it can be very difficult to get a positive identification of B. spathulatum without the assistance of a specialist.
The preferred habitat of B. spathulatum in its northeastern range is stabilized but sparsely vegetated sand dunes and grassy meadows along the shores of the Upper Great Lakes and lower James Bay. In the northwest, it occurs in stabilized maritime dunes, grassy flats, and sparsely vegetated subalpine slopes.
The Minnesota populations of B. spathulatum occur primarily in open and grassy habitats within a forested matrix (Fire-Dependant Forest/Woodland). Actually, the habitat needs of B. spathulatum are probably of lesser importance than the habitat needs of the mycorrhizal fungi upon which it depends for water, minerals, and organic compounds. The particular species of fungus or fungi in question is unknown; however, the general type of fungi that form symbiotic relationships with ferns are themselves dependent on trees and are ubiquitous in healthy forest ecosystems.
The sites in Crow Wing County are associated with drained sediment basins that had previously been used to dispose of mine tailings. Over the past 30-50 years, the basins have evolved into young forests (Fire-Dependent Forest/Woodland), with scattered groves of early successional tree species and a patchy ground-layer of grasses and broad-leaved forbs.
The fact that the basins were man-made, coupled with how rapidly the species was able to colonize them, leads us to believe that a stable source of propagules may occur in more natural habitats nearby. This is supported by the occurrence of the species in natural habitats in other parts of its range, including grassy meadows and sand dunes along lake and maritime shores, grassy riverbanks, shrub-grassland complexes, and subalpine slopes.
Biology / Life History
Very little research has been done on the specific biology and life history of B. spathulatum, though inferences can be drawn from its morphological structure and habitat and from what is known about closely related species. It appears to reproduce only by spores that are produced every year (or at least every year) that growth appears above ground. The spores are spread by wind but under most circumstances probably disperse no more than a few meters. The spores are probably carried below the surface of the ground by water moving downward through pores in the soil. The spores develop into gametophytes (an underground stage), which in turn produce sporophytes (the above-ground stage). It is unknown how long the sporophyte stage survives, though 5 to 10 years is a reasonable estimate.
Peck et al. (1990) determined that more than 90% of spores released by Botrychium virginianum (rattlesnake fern) were deposited within 5 meters (16 feet) of the source plant. It can be hypothesized that spores from B. spathulatum, a much smaller plant than B. virginianum, would disperse a shorter distance. Keep in mind, however, that even 1% of the spores produced by a typical moonwort is a very large number (thousands) of potential propagules (Zika and Farrar 2009).
A number of observations strongly suggest that Botrychium rely heavily, if not entirely, on their mycorrhizal partner for carbohydrates, minerals, and water. With mycorrhizal fungi as an intermediary, Botrychium have greatly reduced direct interaction with their environment (Farrar 2011).
Conservation / Management
Like most moonwort species, B. spathulatum is disturbance-dependent, and it tends to occur in open to partially open habitats. Habitat conditions at known sites in Minnesota are in a state of flux, or at least in a state of vegetational succession. In the absence of natural disturbances (e.g., wildfire, floods, rock slides, and blowdowns) that periodically delay or restart succession, these habitats will turn into more mature forested habitats that are unsuitable for B. spathulatum. It should be noted that the intensity, scale, and frequency of disturbance needed for the perpetuation of the habitat is not yet known, and it would be incorrect to assume that all types of disturbance are beneficial. Natural and man-made disturbances can have very different effects. For example, very intense disturbances, such as those associated with development projects or heavy machinery use, may eliminate favorable habitat conditions for this species.
Based on this analysis, it seems prudent for conservation purposes to assume a metapopulation model for Botrychium population dynamics. In this model, individual populations have a finite lifespan, but their extinction is continuously balanced by the establishment of new populations. Although individual populations in this model may be somewhat transient, it remains important to maintain their viability for as long as possible because they are the source of spores that will establish new populations in appropriate habitat. It is equally important to maintain unoccupied suitable habitat as sites for new populations (Farrar 2011). Maintenance of suitable habitat may be dependent on landscape level dynamics, in which patches of open habitats are continually created and lost by disturbances of varying degrees.
Best Time to Search
It is characteristic for moonworts to appear above ground for only brief periods; in dry years, they may be seen for only a few weeks; and in very dry years, they may not appear at all (Wagner and Wagner 1990). Predicting exactly when B. spathulatum will be at its peak is difficult; but, if it happens at all, it will likely be during the month of June.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Chadde, S, and G. Kudray. 2003. Conservation assessment for Spoon-leaf Moonwort (Botrychium spathulatum). United States Forest Service, Eastern Region, Milwaukee, Wisconsin. 37 pp.
Farrar, D. R. 2011. Systematics and taxonomy of the genus Botrychium. <http://www.public.iastate.edu/~herbarium/botrychium.html>. Accessed 13 February 2013.
Johnson-Groh, C., C. Riedel, L. Schoessler, and K. Skogen. 2002. Belowground distribution and abundance of Botrychium gametophytes and juvenile sporophytes. American Fern Journal 92(2):80-92.
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.
Peck, J. H., C. J. Peck, and D. R. Farrar. 1990. Influences of life history attributes on formation of local and distant fern populations. American Fern Journal 80(4):126-142.
Wagner, W. H., Jr., and F. S. Wagner. 1990a. Notes on the fan-leaflet group of moonworts in North America with descriptions of two new members. American Fern Journal 80(3):73-81.
Wagner, W. H., Jr., and F. S. Wagner. 1990b. Moonworts (Botrychium subg. Botrychium) of the Upper Great Lakes region, U.S.A. and Canada, with descriptions of two new species. Contributions from the University of Michigan Herbarium 17:313-325.
Wagner, W. H., Jr., and F. S. Wagner. 1993. Botrychium. Pages 86-101 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York.
Zika, P. F., and D. R. Farrar. 2009. Botrychium ascendens W. H. Wagner (Ophioglossaceae) in Newfoundland and notes on its origin. American Fern Journal 99(4):249-259.