The EquisetumSpecies (Horsetails) of the British Isles


L. Watson and M. J. Dallwitz

Equisetum fluviatile L.

“Water Horsetail”.

E. limosum L.; E. heleocharis Ehrh.

The rhizomes light brown, glabrous, smooth, with black roots; bearing tubers (according to Le Maout & Decaisne), or not tuberous (according to Goebel). The shoots all green and alike vegetatively, the sterile and cone-bearing shoots emerging at the same time.

The main stems 50–140 cm high; 2–12 mm in diameter; more or less erect; smooth; bearing whorls of slender branches at the nodes (around the middle), or simple; dying down in autumn. The main stem internodes 10–30 grooved; grooves fine, the ribs between them not prominent. The main stem internodes with a central hollow; central hollow much more than half the diameter of the internode (4/5 or more); endodermis surrounding the individual vascular bundles. The main stem sheaths green; loose to appressed (somewhat loose); 10–30 toothed (as many as the grooves). The teeth not ribbed; subulate, small (about 1 mm), black tipped. The primary branching asymmetrical. The primary branches numerous; ascending; when present, simple (slender, ascending). The primary branch internodes usually 5 -angled. The primary branch sheaths 4–5 toothed (the teeth moderate, subulate, green or blackish). The first branch internodes about as long as or shorter than the subtending sheaths. The primary branch internodes hollow. Stomata not sunken.

The cones 1–2 cm long; blunt. Spores released June to July.

Distribution. Europe, from Iceland and arctic Russia to central Spain, Italy, Macedonia and the Caucasus; temperate Asia; North America, from Labrador and Alaska to Virginia and Oregon. Common throughout the British Isles, in shallow water at edges of ponds and lakes and in ditches, less often in fens and marshes, ascending to almost 1000 m.

Classification. Subgenus Equisetum; Section Aestivalia.

Illustrations. • Equisetum fluviatile: from Sowerby and Johnson (1859). • E. fluviatile: as E. limosum, Eng. Bot. 1893 (1886). • 10 British Equisetum species and hybrids: Sowerby and Johnson, 1863. • E. fluviatile: cone, rhizome and prothallus. • E. fluviatile: details of spore development.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. The Equisetum species (horsetails) of the British Isles. Version: 7th March 2015.’.