Botrychium ascendens W.H. Wagner
Basis for Listing
Botrychium ascendens (upswept moonwort) ranges widely across North America, extending from southern Nevada north to Alaska and eastward across Canada to Quebec and Newfoundland and in the United States to northern Minnesota and Vermont (Farrar 2011). In spite of its wide range, it is considered rare and local wherever it occurs (Wagner and Wagner 1986), and it is especially rare in Minnesota. The Minnesota plants, first discovered in 1998, also have special biological significance beyond their obvious rarity.
Genetic analysis of B. ascendens has revealed two distinctive genotypes. The most common and widespread genotype is shared by all known populations in the contiguous western United States, as well as the coastal populations in Alaska, Newfoundland, and Quebec. A second genotype is found in the Minnesota and Vermont plants. The existence of these different genetic entities implies historical and continued isolation of these eastern U.S populations (Farrar 2011).
Given the small number of documented 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 ascendens was designated an endangered species in 2013.
Members of the genus Botrychium (moonworts) typically produce 1 leaf per year. The above-ground portion of a mature leaf is divided into 2 separate parts. One part, bearing an expanded and usually photosynthetic blade, is called the "trophophore", or sterile segment. The other part, bearing numerous globose sporangia, is called the "sporophore", or fertile segment. The trophophore and sporophore are joined into a common stalk or petiole, usually near the base of the blade. The common stalk extends underground to the stem apex, where its base encloses the apical bud.
The aboveground parts of B. ascendens average just 6 -10 cm (2.4-3.9 in.) in height, with about half that height being the common stalk, though it can be as small as 2 cm (0.8 in.). The sporophore is one-third to one-half again as long as the trophophore. The trophophore is bright yellow-green and shiny, with conspicuous veins. It is narrowly oblong-triangular in outline, with up to 6 pairs of strongly ascending segments. The largest pinnae are about 12 mm (0.47 in.) long and 10 mm (0.39 in.) wide, with 2 or 3 major veins entering the pinnae base, and 14-17 vein endings along outer margins of larger pinnae. The margins of the pinnae are deeply and sharply dentate and serrate, often 2- to 5-lobed (Wagner and Wagner 1993).
Plants of B. ascendens are most similar to B. crenulatum (scalloped moonwort), B. minganense (Mingan moonwort), B. spathulatum (spatulate moonwort), and B. campestre (prairie moonwort). Botrychium ascendens differs from these species in its more strongly ascending (upwardly angled) basal pinnae, pinna margins that are sharply dentate to cleft (into 2-4 spreading lobes), a sporophore stalk that is much shorter at maturity than the length of the trophophore but longer than that of B. campestre. The basal pinnae of B. ascendens are cuneate, usually spanning an arc of 90 degrees or less; whereas, basal pinnae of B. crenulatum typically span an arc of nearly 180 degrees (Farrar 2011).
In Minnesota, B. ascendens is primarily a plant of forested regions, though it is usually found in open grassy habitat some distance from dense tree cover. The most common habitat seems to be ecotones between meadows and forests in the Tallgrass Aspen Parklands Province or between lake shores and forests in the Laurentian Mixed Forest Province. Other habitats include grassy openings in forests that were created and maintained by relatively low impact human activities. It has also been found growing in fine sediments that were deposited in iron ore tailings ponds some years after the ponds had been drained. In all settings, look for it in sparse to dense cover of grasses, forbs, and small shrubs.
Biology / Life History
Being ferns, Botrychium (moonworts) have two separate life stages. The relatively large and above-ground sporophyte produces spores that germinate underground and grow into the below-ground gametophyte stage. Each gametophyte produces both sperm and eggs. When a sperm is released, it swims to an egg with which it fuses to form a zygote, the initial cell of the next sporophyte generation. The sperm from one gametophyte plant may be unable to reach the egg from another gametophyte plant, if it is more than a few millimeters away. However, they are quite capable of fertilizing eggs from the same gametophyte, less than one millimeter away. This union of gametes from the same gametophyte constitutes inbreeding. Although some genetic variation exists among populations of B. ascendens, within-population variation is essentially non-existent. This is likely a consequence of inbreeding (Zika and Farrar 2009).
Peck et al. (1990) determined that more than 90% of spores released by B. virginianum (rattlesnake fern) were deposited within 5 meters (16 feet) of the source plant. It can be hypothesized that spores from B. ascendens, a much smaller plant than B. virginianum, would disperse a shorter distance. It must be recognized, however, that even 1% of the spores produced by a typical moonwort is a very large number (thousands) of potential propagules.
A number of observations strongly suggest that species of Botrychium 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).
Conservation / Management
Like most moonwort species, B. ascendens is disturbance-dependent, and it tends to occur in open to partially open habitats. Habitat conditions at the Minnesota sites 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. ascendens. It must be noted, however, that the intensity, scale, and frequency of disturbance required for the perpetuation of a population is not yet known, and it would be incorrect to assume that all types of disturbance are beneficial. Very intense disturbances, such as those associated with development projects or heavy machinery use, may eliminate favorable habitat conditions for the species. The persistence of the species in any given area is likely dependent on landscape level dynamics in which patches of suitable habitats are continually created and lost by disturbances of varying degrees.
These observations, as well as published reports (Farrar 2011), provide support for 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 at other locations. Although individual populations may have a relatively short existence, 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).
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 1990a). Predicting exactly when B. ascendens will be at its peak is difficult; however, if it happens at all, it will likely be in the month of June.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Beatty, B. L., W. F. Jennings, and R. C. Rawlinson. 2003. Botrychium ascendens W. H. Wagner (trianglelobe moonwort), Botrychium crenulatum W. H. Wahner (scalloped moonwort), and Botrychium lineare W. H Wahner (narrowleaf grapefern): a technical conservation assessment. United States Forest Service, Rocky Mountain Region, Golden, Colorado. 60 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.
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.
Wagner W. H., Jr., and F. S. Wagner. 1986. Three new species of moonworts (Botrychium Subg. Botrychium) endemic in western North America. American Fern Journal 76(2):33-47.
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.