Rare Species Guide

  Basis for Listing

It was not until 1990 that Botrychium acuminatum (tailed grapefern) was recognized as distinct from the common B. matricariifolium (matricary grapefern) (Wagner and Wagner 1990). Since that time, only a handful of specimens have been confirmed as B. acuminatum, including two in the Arrowhead region of Minnesota (Northern Superior Uplands Section). The other confirmed specimens are from northern Michigan and adjacent parts of Ontario. These identifications are considered reliable because they were confirmed by W. H. Wagner himself, who not only described the species but was considered the leading authority on the genus Botrychium of the twentieth century.

In recent years, the genetic uniqueness of B. acuminatum has been questioned. Farrar (2011) lists it as one of the “Problematic taxa”.  His research revealed no genetic differences between B. acuminatum and B. matricariifolium, even though the type specimen of B. acuminatum shows distinctive morphology. Furthermore, Farrar concluded from a broader sampling of B. matricariifolium that there is a continuum of morphological variation from the “acuminatum” type to typical B. matricariifolium. 

The apparent rarity of this species may warrant a status of endangered or threatened; however, that would imply a level of knowledge that does not currently exist. Based on the relative newness of the discovery of this species and the uncertainty of its genetic uniqueness, in 2013 the status of special concern was deemed warranted.

  Description

There are known to be at least 11 species of Botrychium (moonworts) in Minnesota (MNDNR 2015). All are small ferns, with a single leaf. As a genus, they are easy to recognize with practice. But the species all look very much alike, and telling them apart often requires the help of a specialist. The following description is highly technical; unfortunately, any simplification of the details would not make the identification of an unknown specimen any easier.

Trophophore stalk is 0-2.0 cm (0-0.8 in.) long and 0.1 to 0.5 times the length of the trophophore rachis; blade dull, glaucescent, ovate-oblong, 1-pinnate, up to 6 x 5 cm (2.4 x 2.0 in.) and firm. Pinnae up to 6 pairs, spreading to ascending, mostly separated by pinna width, with distance between 1st and 2nd pinnae not or (only) slightly more than between 2nd and 3rd pairs; basal pinna pair approximately equal in size and cutting to next adjacent pair, narrowly oblanceolate to linear-lanceolate; simple to irregularly divided to tip, margins commonly ± entire and with 1 to several shallow and irregular lobes; apex acuminate; venation pinnate. Sporophores 1-2 pinnate and 1.4 to 2 times length of trophophore (Wagner and Wagner 1993).

  Habitat

The preferred habitat of B. acuminatum in Minnesota is poorly known. Only two occurrences have been documented, both from somewhat ruderal and grassy habitats near lakes in the forested region of the state (North Shore Highlands and Border Lakes Subsections). In all likelihood, this plant is a forest “edge species”, meaning it occurs along natural or human-created forest edges, where it gets full or partial sunlight.

  Biology / Life History

Very little, if anything, is known about the biology of B. acuminatum. It is perhaps too recently described and too rare to have been the subject of careful investigation. However, some reasonable assumptions can be drawn from what is known about ferns in general and the genus Botrychium in particular. Being ferns, all species of Botrychium have two separate life stages. The relatively large and above-ground sporophyte stage produces spores that germinate underground and grow into the below-ground gametophyte stage. The gametophytes, in turn, produce the sporophytes. Since an unknown portion of any Botrychium population exists underground in the gametophyte stage, it is not possible to get a census by merely counting the visible plants.

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. acuminatum, 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. For this reason, Botrychiums have very limited direct interaction with their environment (Farrar 2011).

  Conservation / Management

Too little is currently known about this species and its habitat requirements to offer any useful summary of conservation and management considerations.

  Best Time to Search

Botrychiums are identified by the shape of their leaf, which, in the case of B. acuminatum, appears above ground in midsummer and dies back in the fall (Wagner and Wagner 1993). Based on this, mid-June through early July are probably the best times to search for this species.

  Authors/Revisions

Welby R. Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Farrar, D. R. 2006. Systematics of moonworts Botrychium subgenus Botrychium. . Accessed 09 Mar 2009.

Farrar, D. R. 2011. Systematics and taxonomy of the genus Botrychium. <http://www.public.iastate.edu/~herbarium/botrychium.html>. Accessed 12 October, 2015.

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. 2015. MNTaxa: the state of Minnesota vascular plant checklist. <http://www.dnr.state.mn.us/eco/mcbs/plant_lists.html>. Accessed 11 October, 2015.

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.

Penskar, M. R., and P. J. Higman. 2001. Special plant abstract for Botrychium acuminatum (acute-leaved moonwort). Michigan Natural Features Inventory, Lansing, Michigan. 2 pp.

Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.

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, New York.