Equisetum sylvaticum is a rhizomatous, twice-branched member of the horsetail family (Equisetaceae), found in lowland forests, meadows and bogs. Equsetum sylvaticum grows from a light brown rhizome. The sterile and fertile stems are of two kinds. The sterile stems grow up to 60 cm tall in Denali, are 14 mm in diameter, and the central cavity is one-half the diameter of the stem. There are inflated reddish brown sheaths on the stems. The branches have secondary branches which are arched and drooping. The fertile stems are up to 14 cm tall often with short branches when the spores are formed. The cones are peduncled and up to 3 cm long. Equisetum sylvaticum is distinguished from the similar E. pratense and E. arvense by its elegant doubly-branched habit with drooping branches. Equisetum sylvaticum is the only horsetail in Denali that has compound branches.
The cones of Equisetum sylvaticum mature and shed spores in late spring.
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.
Refer to Equisetum arvense for the known uses of horsetails and scouring rushes in general. Moerman (1998) reports that an infusion of the stems and branches of E. sylvaticum was used by the Eskimo to stop internal bleeding; a poultice was used externally for the same purpose by the Menominee, and it was used as a kidney aid by the Menominee and Ojibwa.
Equisetum sylvaticum is a widespread circumpolar species. Outside of North America it occurs in Europe, northern Asia, northeast China, and Japan. It occurs east of the Coast-Cascade Mountains in British Columbia and in the rest of the Canadian Provinces. It occurs in Alaska, and the northern part of the lower forty-eight states north of a line drawn from the 46th parallel on the west coast (southern Washington) to approximately the 36th parallel on the east coast (Virginia). In Alaska, E. sylvaticum occurs throughout the state south of the Brooks Range (except for the Aleutians). This species occurs on both sides of the Alaska Range in the park. It is the second most common species in the genus in the park after E. arvense.
Throughout its North American range, Equisetum sylvaticum occurs at altitudes 0-2800 m. It occurs at 91-994 m in Denali, at an average of 434 m, with most occurrences at 300-700 m, but with the greatest coverage in plots at elevations less than 300 m. Next to E. fluviatile it has the lowest maximum elevational extent (994 m). More than half (57%) of the occurrences were on flat terrain, 24% were on south-facing slopes and 19% were on north facing slopes. For both incline classes, most occurrences were on mild slopes (8-15 degrees).