Equisetum palustre is a rhizomatous, branched member of the horsetail family (Equisetaceae) found growing in wetlands and meadows. Horsetails have rush-like stems with ridges of siliceous tubercles and produce spores in cones. Equisetum palustre grows from shiny black to brown rhizomes, up to 70 cm tall, and with 1-3 mm thick stems. The central cavity of the stem is about one-sixth the stem diameter. The fertile and sterile branches are similar; they may be branched or unbranched with irregular whorls. The first internode of the branches is shorter than the corresponding sheath. The cones are 1-3.5 cm long, rounded at the tip and short pedunculate. Equisetum palustre is most similar to E. fluviatile except for its generally shorter stature, much narrower central cavity of the stems and stem sheaths white margined teeth rather than dark brown as in E. fluviatile.
The cones of Equisetum palustre mature and shed spores in the summer.
Equisetum species reproduce sexually and asexually. Sexual reproduction is limited by ecological conditions. hygroscopic spores are produced, but they are short lived and germinate depending on humidity. Once germinated, the gametophyte produced by spores requires a recently exposed substrate to become established. Asexual reproduction is by rhizomatous growth which can be rapid in favorable moist and disturbed habitats. Reproduction also occurs by fragmentation of rhizomes and stems. Clones may spread rapidly, and since usually they are sterile, may establish characters indicating taxonomic differentiation.
Marsh horsetail is a host species to nine known insect species: two beetle species (Hippuriphila modeeri and Grypus equiseti), and seven sawfly species (Dolerus aericeps, D. cothurnatus, D. ferrugatus, D. germanicus, D. gessneri, Loderus eversmannii, and L. vestigialis) (Biological Records Centre 2008). Six fungal species are known to infect the live and dead stems of marsh horsetail: Hymenoscyphus rhodoleucus, Mycosphaerella equiseti, Phoma epitricha, Psilachnum inquilinum, Stagonospora equisiti, and Stamnaria persoonii (Peat et al. 2015).
Refer to Equisetum arvense for the known uses of horsetails and scouring rushes in general. The Ojibwa used an infusion or decoction of E. palustre for stomach or bowel troubles in general and as laxative.
Equisetum palustre is an incompletely circumpolar species. Outside of North America it occurs in Eurasia south to the Himalayas and northern China, Korea and Japan. In North America, it occurs in Alaska, all of Canada and south to approximately the 40th parallel (Vermont, Connecticut, Missouri, Illinois, Montana, North Dakota, Idaho and California). It occurs in most of Alaska, except for the northern coastal regions, the Aleutians and the Panhandle. It occurs on both sides of the Alaska Range in Denali but is the least common member of this the genus in the park, occurring in less than 1% of all measured plots.
Equisetum palustre is primarily a plant of the lowlands. Throughout its North American range, it occurs at altitudes 0-1500 m, in Denali it occurs at 74-1022 m, and at an average of 447 m. All occurrences but three were on flat terrain (less than five degree incline).
Marsh horsetail grows in standing water in ponds, marshes, swamps, ditches, stream banks, muskeg and in wet forests and meadows. It tolerates a wide range of soil types and substrates, provided that they are permanently damp and base-rich (Botanical Society of the British Isles 2015).