- Scientific name: Eleocharis intermedia Schult
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Threatened (MA Endangered Species Act)
Description
The matted spike-sedge (Eleocharis intermedia) is a small (from about 5-25 cm [2-10 in] tall), densely tufted, annual herb with thin, wiry stems. Although the matted spike-sedge and the other spike-sedges (also called spike-rushes) superficially resemble the group of plants called “rushes,” they do not belong to the rush Family, and are actually members of the sedge Family. The spike-sedges have a single, tight cluster of inconspicuous flowers (a “spike”) at the apex of each stem. The stems of spike-sedges appear leafless, and in fact these plants do not have leaf blades (the expanded part of the leaf), only leaf sheaths (the part which surrounds the stem). The matted spike-sedge has very slender, round stems with a groove running up them. The stems are usually all clumped together in somewhat of a mat, with some stems reclining horizontally and some standing erect. The stems within a mat are typically of different lengths.
To positively identify the matted spike-sedge and other spike-sedges (genus Eleocharis), a technical manual should be consulted. It is usually necessary to look at the tiny fruits of the plant under magnification to distinguish the species of spike-sedge. Members of this genus possess a type of fruit called an “achene,” which is hard and nut-like and does not split open to release its single seed. Achenes in the spike-sedges are topped by a protuberance (called a “tubercle”), which varies in shape, size, and texture among species.
The tiny achene (only about 1 mm [0.04 in] wide) of the matted spike-sedge matures in mid- to late summer, and is light brown to pale olive or yellow in color. It is three-sided, and appears smooth under a hand lens (slightly bumpy under a microscope). The tubercle is relatively narrow in this species and looks something like a small dunce’s cap on top of the achene.
There are many common spike-sedges or spike-rushes that could be confused with the matted spike-sedge. A common spike-sedge with very slender stems that forms mats or carpets is the needle spike-rush (Eleocharis acicularis). It is distinguished from the matted spike-sedge by having a long, gray achene that is roundish in cross-section, rather than strongly triangular. The slender spike-rush (Eleocharis tenuis) is thin-stemmed, but the stems are usually 4- to 8-angled (instead of round) and are scattered or only loosely clustered. The achenes of the Slender spike-rush are rough or pitted in appearance when observed under a hand-lens. The soft-stemmed spike-rush (Eleocharis obtusa), a common associate, is another tufted annual that differs from the matted spike-sedge in having lens-shaped achenes (instead of triangular) and in its more robust appearance. Its stems are usually taller and thicker than the delicate, thread-like stems of the matted spike-sedge.
Life cycle and behavior
Matted Spike-sedge is an annual species which forms dense tufts. It is not rhizomatous. It is wind pollinated with mature achenes from early July through mid-September. (Seymour 1969) As this species grows in and near water, its seeds may be moved by flowing water to new locations.
Population status
The matted spike-sedge is listed under the Massachusetts Endangered Species Act as Threatened. 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. Matted spike-sedge has 12 populations that have been verified since 1999 in Berkshire, Franklin and Hampshire Counties, and 17 that have not been relocated in the past 25 years.
Distribution in Massachusetts. 1999-2024. Based on records in the Natural Heritage Database.
Distribution and abundance
Matted Spike-sedge is known from New Brunswick and Quebec west to Ontario and Minnesota, its range than extends south to Mississippa and Virginia with a disjunct pattern. It is considered rare in many states. In New England, it is critically imperiled in New Hampshire, imperiled in Massachusetts, and vulnerable in Vermont. Neither Connecticut or Maine have ranked it, and it does not occur in Rhode Island. (NatureServe 2025)
Habitat
The matted spike-sedge is typically found in marshes, freshwater mudflats, or in other wet areas with muddy substrates. In Massachusetts, this plant is found on muddy, alkaline riverbanks and pond shores, usually during periods of low water when mud is exposed. Plants found in association with the matted spike-sedge in Massachusetts include false pimpernel (Lindernia dubia), nodding bur-marigold (Bidens cernua), rice cut-grass (Leersia oryzoides), and soft-stemmed spike-sedge (Eleocharis obtusa).
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Conservation
As for many rare species, exact needs for management of matted spike-sedge are not known. The following comments are based primarily on observations of populations in Massachusetts. Because this plant occurs in freshwater marsh mud-flats or muddy soils, proximity to a freshwater source such as a river, pond, or stream is necessary. Regular fluctuation in water level appears to benefit the species, which can be found on exposed mud during low-water years. Low-level disturbance provided by gentle wave action and/or regular flooding is important to maintain the relatively open, muddy conditions in which the intermediate spike-sedge thrives.
References
Arsenault, Matt, Glen H. Mittelhauser, Don Cameron, Alison C. Dibble, Arthur Haines, Sally C. Rooney, and Jill E. Weber. 2013. Sedges of Maine, A Field Guild to Cyperaceae. University of Maine Press, Orono, Maine.
Haines, A. 2011. Flora Novae Angliae – a Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. New England Wildflower Society, Yale Univ. Press, New Haven, CT.
NatureServe. 2025. NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. Accessed: 5/23/2025.
POWO (2025). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; https://powo.science.kew.org/ Accessed: 5/24/2025.
Seymour, Frank C. 1969. The Flora of New England, First edition. Charles E. Tuttle Company, Inc. Tokyo, Japan.
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| Date published: | May 7, 2025 |
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