- Scientific name: Equisetum scirpoides Michx.
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Special Concern (MA Endangered Species Act)
Description
Dwarf scouring rush, Equisetum scirpoides, is a member of the horsetail family (Equisetaceae). It is 10-20 cm (4-8 in) tall, evergreen and appears as a dark tuft of wiry stems. Dwarf scouring rush has slender stems which may curve upward or lie flat along the ground and widely branching rhizomes. The stem has 3 to 4 broad and deeply concave ridges. Triangular sheaths surrounding the stems are 3-4 mm (<1 in) long and have 3 or 4 teeth. Small (3-5mm [0.12-0.2 in]), dark cones develop in late summer.
The wiry form of the plant. Photo Credit: Arthur Haines, Native Plant Trust
Closeup of cones. Photo Credit: Arthur Haines, Native Plant Trust
Life cycle and behavior
Dwarf Scouring rush is a perennial plant. Its many stems connect with an underground rhizome, which produce both fertile and non-fertile stems. Fertile ramets tend to be a bit straighter than the non-fertile ones. Mature fruit (spores) may be found in late summer.
Closeup sheath and stem. Photo Credit: Peter M. Dziuk, MinnesotaWildflowers.info.
Closeup of stem size and ribbing. Photo Credit: Karro Frost
Population status
Dwarf scouring rush is listed under the Massachusetts Endangered Species Act as a species of special concern. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors.
Thirty-four populations of dwarf scouring rush have been verified as extant since 1999 in Berkshire, Franklin and Hampshire Counties. Six additional populations have not been recently relocated. One reason for its rarity in Massachusetts is because it is near the southern edge of its range. It is considered rare in most of the states on the southern edge of its distribution. Globally, NatureServe ranks dwarf scouring rush as G5, secure.
Distribution and abundance
Dwarf scouring rush has a circumboreal distribution. In North America, it extends across Canada and south into Connecticut, west through Illinois, Iowa, South Dakota, and Wyoming and then into Washington.
In New England, dwarf scouring rush is critically imperiled in Connecticut, vulnerable in Massachusetts, secure in Vermont, and not ranked in Maine and New Hampshire. It is not known to occur in Rhode Island.
Distribution in Massachusetts. 1999-2024. Based on records in the Natural Heritage Database.
Habitat
Dwarf scouring rush is found on mossy hummocks, moist banks and seepy wooded slopes and hillsides with springs and streams: they are often in ecotones between upland and wetland sites. Dwarf scouring rush is known to grow in subacidic and acid glacially derived soil.
Associated species often include tree elements of the northern hardwood forest including red maple (Acer rubrum), sugar maple (A. saccharum), northern white cedar (Thuja occidentalis), white ash (Fraxinus americana), eastern hemlock (Tsuga canadensis), and yellow birch (Betula alleghaniensis). The hemlock provides shade and a cool habitat. Shrubs may include striped maple (Acer pensylvanica), spicebush (Lindera benzoin), and low raspberry (Rubus pubescens). The herbaceous layer may be sparse, however, a variety of native species have been reported in the area of dwarf scouring rush populations including cinnamon fern (Osmunda cinnamomea), Arctic sweet coltsfoot (Petasites frigidus), small Enchanter’s nightshade (Circaea alpina), other horsetails, and liverworts and mosses.
Healthy habitats are vital for supporting native wildlife and plants. Explore habitats and learn about conservation and restoration in Massachusetts.
Threats
Invasive species and development are the primary threats to this species. Many of the occurrences of dwarf scouring rush have invasive species near the population. Competition from non-native invasive species can be a threat through shading and loss of space for the native species.
Additionally, road development is a threat due to habitat loss, disturbance, and alterations in hydrology. Several populations of dwarf scouring rush are near roads: widening of roads and creation of both formal and informal pull-off sites should be reviewed with regard to the effects on the dwarf scouring rush.
In many populations, the hemlock overstory may be damaged and thinned by wooly adelgids, an invasive species that infects and kills hemlock trees. Similarly, ash overstories may be damaged and thinned by emerald ash borer, another invasive that infects and kills ash trees. These invasive species’ influences on the forest community could potentially alter hydrology and shade levels on the forest floor, diminishing habitat conditions for populations of dwarf scouring rush.
Conservation
Survey and monitoring
Dwarf scouring rush is an evergreen species and can be found year-round. Stems are small, connected underground, and difficult to count. Counting clumps of stems if spread out or estimating area covered by square feet or square meters is best.
Management
Monitoring and removal of competing vegetation should be considered as a management strategy where appropriate. All active management of rare plant populations (including invasive species removal) is subject to review under the Massachusetts Endangered Species Act and should be planned in close consultation with the MassWildlife’s Natural Heritage & Endangered Species Program.
Research Needs
Many populations of scouring rush are in or near natural communities of ash and hemlock. The hemlock overstory may be damaged and thinned by wooly adelgids. In addition, ash trees are at risk of damage and thinning due to emerald ash borer activity. Because tree thinning or damage can alter hydrology and canopy shade levels, it is possible that dieback of trees and canopy thinning caused by invasive pests pose a more significant threat to the species than is currently known. More research is needed to determine the extent that these forest changes will affect scouring rush.
References
Cobb, Boughton, et al. A Field Guide to Ferns and Their Related Families: Northeastern and Central North America. 2nd ed, Houghton Mifflin Co, 2005. The Peterson Field Guide Series.
Equisetum Scirpoides - Species Page - NYFA: New York Flora Atlas. https://newyork.plantatlas.usf.edu/plant.aspx?id=1297. Accessed 26 Mar. 2026.
Equisetum Scirpoides (Dwarf Scouring-Rush): Go Botany. https://gobotany.nativeplanttrust.org/species/equisetum/scirpoides/. Accessed 26 Mar. 2026.
POWO (2026). "Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; https://powo.science.kew.org/ Retrieved 26 March 2026.
Gleason, Henry Allan, and Arthur Cronquist. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. 2nd ed, New York Botanical Garden, 1991.
Gray, Asa, and Merritt Lyndon Fernald, editors. Gray’s Manual of Botany: A Handbook of the Flowering Plants and Ferns of the Central and Northeastern United States and Adjacent Canada. 8. (centennial) ed., Corrected printing, Van Nostrand, 1970.
Magee, Dennis W., and Harry E. Ahles. Flora of the Northeast: A Manual of the Vascular Flora of New England and Adjacent New York. 2nd ed, University of Massachusetts Press, 2007.
NatureServe Explorer 2.0: Equisetum Scirpoides. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.152751/Equisetum_scirpoides. Accessed 26 Mar. 2026.
NORM Phenology Information. Native Plant Trust, 2014.
Sessa, Emily B. 2024. Ferns, Spikemosses, Clubmosses, and Quillworts of Eastern North America. Princeton University Press, Princeton, NJ.
Contact
| Date published: | May 7, 2025 |
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| Last updated: | May 5, 2026 |