The EquisetumSpecies (Horsetails) of the British Isles
The rhizomes light brown, smooth and shiny, hairy; bearing tubers, or not tuberous. The shoots distinguishable as fertile and sterile: both types produced at the same time, but those bearing cones remaining non-green and unbranched until after spore dispersal, and only later becoming green and branching so as to resemble the sterile stems vegetatively.
The main stems 10–80 cm high (sterile), or 10–40 cm high (fertile); 1–4 mm in diameter; erect; bright green; slightly rough to smooth; bearing whorls of slender branches at the nodes (the branches numerous, fewer and shorter on the fertile stems), or simple (perhaps occasionally, when fertile); dying down in autumn. The main stem internodes not swollen; 10–18 grooved (in sterile stems). The main stem internodes with a central hollow; central hollow about half the diameter of the internode to more than half the diameter of the internode (a half to two thirds); endodermis comprising a single layer outside the ring of vascular bundles. The main stem sheaths green or greenish; 5–10 mm long; ostensibly 3–6 toothed (seemingly having joined teeth, these represented by the 3–6 broad, subacute, brown lobes). The teeth about 3 ribbed; persistent. The primary branching symmetrical. The primary branches numerous (10 to 16 or more per whorl); drooping (towards their ends); delicately secondarily branched (at least proximally, lending the plant its characteristic elegance). The primary branch internodes 3–4 grooved; 3–4 grooved. The primary branch sheaths 3–4 toothed (the teeth long, subulate). 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 1.5–2.5 cm long; blunt. Spores released April to May.
Distribution. Europe, from Iceland and Scandinavia to northern Spain, northern Italy, Crete and the Caucasus; temperate Asia; North America from Newfoundland and Alaska to Virginia and Iowa; southern Greenland. Throughout the British Isles except for some midland and southern counties and the Channel Isles; associated with acid soils in damp woods and moors, ascending to about 1000 m.
Classification. Subgenus Equisetum; Section Subvernalia.
Illustrations. • E. sylvaticum (Sowerby and Johnson). • 10 British Equisetum species and hybrids (Sowerby and Johnson). • E. sylvaticum: fertile and sterile stems, and rhizome.
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’.