The EquisetumSpecies (Horsetails) of the British Isles
The rhizomes dark brown to black, dull, hairy; bearing tubers (often, these ovoid), or not tuberous. The shoots conspicuously dimorphic: the cone-bearing stems thick, unbranched, brown and non-assimilating, appearing in early spring and withering before the emergence of the sterile, branched, green, persistent ones (or rarely, the fertile stems persist and become green).
The brown, non-assimilating fertile stems 10–25 cm high; about 4–6 mm in diameter (erect, smooth, somewhat succulent); with only 4 to 6 relatively distant sheaths; sheaths 6–12 toothed.
The main stems of assimilating shoots, 20–80 cm high; 3–5 mm in diameter; erect to decumbent; bright green; slightly rough; bearing whorls of slender branches at the nodes; dying down in autumn. The main stem internodes 6–19 grooved; grooves deep, with prominent ridges between. Central hollow much less than half the diameter of the internode to about half the diameter of the internode (from one third to two thirds its diameter); endodermis comprising a single layer outside the ring of vascular bundles. The main stem sheaths pale; about as broad as long ((1-)3–8(-10) mm long, 1–9 mm wide); 6–19 toothed (as many teeth as grooves, but the teeth often more or less cohering in pairs). The teeth one ribbed (the ribs reaching to their tips); subulate, acute, green with blackish tips. The primary branching symmetrical. The primary branches numerous (about ten or twelve); spreading to drooping; usually simple (sometimes with a hint of secondary branching). The primary branch internodes (3–)4 grooved. The primary branch sheaths 4 toothed (the teeth triangular-lanceolate, acuminate, somewhat spreading, pale). The first branch internodes at least as long as the subtending sheaths, at least on the upper parts of the stem. The primary branch internodes solid. Stomata not sunken.
The cones 1–4 cm long; blunt. Spores released in April.
Distribution. Arctic and north temperate, from Greenland to S. Spain, Crete, central China, Virginia, Alabama and California. Common throughout the British Isles, in fields, hedgebanks, waste land, dune-slacks, etc., ascending to nearly 1000 m.
Classification. Subgenus Equisetum; Section Vernalia.
Illustrations. • Equisetum arvense (from Sowerby and Johnson). • Equisetum arvense (from Curtis). • 10 British Equisetum species and hybrids (Sowerby and Johnson, 1863). • Equisetum arvense L.: sporophyte epidermis, prothalli.
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: 21st June 2009. http://delta-intkey.com’.