Botrychium angustisegmentum (Pease & Moore) Clausen
Narrow Triangle Moonwort
Botrychium lanceolatum var. angustisegmentum, Botrychium lanceolatum ssp. angustisegmentum
Basis for Listing
Botrychium angustisegmentum (narrow triangle moonwort) ranges across northeastern and north-central U.S. and adjacent parts of Canada, reaching the western periphery of its range in Minnesota. The species was first collected in the state in 1918 in Morrison County. Its status remained a mystery until it was collected again in 1992. Several years of focused searches have provided a clearer idea of this species' distribution and habitat preferences. While B. angustisegmentum has been found throughout the Laurentian Mixed Forest Province, it seems to occur in only a small percentage of the seemingly suitable forest habitats that were searched. Although still believed to be rare, the number of recent site records indicate this plant may not be as rare as first thought. Perhaps it was overlooked in the past because of its small size and habit of not emerging above ground every year. Nonetheless, many of the locations where it is found are under threat of habitat loss or alteration. Botrychium angustisegmentum was listed as a threatened species in Minnesota in 1996.
Botrychium angustisegmentum is typically 6.0-15.0 cm (2.4-5.9 in.) tall. It consists of a single leaf with a fertile portion, called the sporophore, and separate sterile section, called the trophophore. The two sections are joined at the petiole, which is sometimes called the common stalk. The trophophore is dark green, shinny, and triangular in shape. It has 2-5 pairs of pinnatifid pinnae, the lowest pair are the largest, and they gradually decrease in size towards the apex, which gives the whole blade its triangular shape. Botrychium angustisegmentum can be distinguished from other species of Botrychium, of which there are many, by the triangular shape of the trophophore (Wagner and Wagner 1993).
In Minnesota, B. angustisegmentum prefers moist, shady, mature northern hardwood forests, particularly in low areas. It usually occurs with Acer saccharum (sugar maple), Betula alleghaniensis (yellow birch), Fraxinus pennsylvanica (green ash), Fraxinus nigra (black ash), Quercus rubra (northern red oak), Tilia americana (basswood), and sometimes Thuja occidentalis (northern white cedar). The understory can be rather open and the ground cover often sparse with Athyrium filix-femina var. angustum (lady fern) and other Botrychium species, especially B. matricariifolium (daisy-leaved moonwort). Botrychium angustisegmentum populations often occur as a few scattered individuals, but occasionally 50 or more can be found in a single site.
Biology / Life History
It takes up to seven years for a B. angustisegmentum spore to develop into a plant that produces an above-ground leaf. Although the plant usually produces one leaf each year, that leaf may not emerge above ground. Leaves of this species emerge in the spring and are divided into a sterile photosynthetic portion and a fertile spore-bearing portion. Spores of the fertile portion mature slowly through the summer, changing to a noticeable gold color by late summer. The aboveground portion of the plant is killed by frost in the fall, sometimes as late as October.
Conservation / Management
Botrychium angustisegmentum appears to be very sensitive to disturbances within its forest habitat, more sensitive than most Botrychium species. The most often cited problems result from: loss of the humus layer caused by non-native earthworms, damage caused by timber harvesting, the effects of road building, and land use changes that affect drainage. In general, any activity that results in the creation of significant gaps in the overstory canopy would likely be deleterious to this species and its habitat. The term significant gap, in this case, means anything greater in extent or more frequent in time than single tree gap phase dynamics, which is part of the normal range of variability in mature forests. Significant gaps can result from timber management activity, even selection harvesting. This can increase solar energy reaching the forest floor, thereby warming and drying the soil. This could result in a major shift in floristic composition, which will likely not favor B. angustisegmentum. Small local populations of fewer than ten individuals may be particularly at risk (U.S. Forest Service 2000).
Best Time to Search
The presence of sporangia is not needed to confirm the identification of Botrychium angustisegmentum; the shape of the sterile portion of the leaf (the trophophore) is usually enough. For this reason, the best time to search is when the leaf is at its peak, from early June to September.
Conservation Efforts in Minnesota
Although a number of B. angustisegmentum populations occur on State Forest lands and county-owned lands, they may be threatened by intensive timber harvest.
Welby R. Smith (MNDNR), 2021
(Note: all content ©MNDNR)
References and Additional Information
Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.
Stensvold, M. C. and D. R. Farrar. 2016. Genetic diversity in the worldwide Botrychium lunaria (Ophioglossaceae) complex, with new species and new combinations. Brittonia 69(2):148-175.
United States Forest Service. 2000. Population viability assessment in forest plan revision. Questions for plant population viability assessment panel: Botrychium lanceolatum. United States Forest Service, Region 9, Superior National Forest, Duluth, Minnesota.
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.