The EquisetumSpecies (Horsetails) of the British Isles
E. maximum auct.
The rhizomes dark brown, rough; bearing tubers (often, these pear-shaped), 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.
The brown, non-assimilating fertile stems 20–40 cm high; with numerous sheaths and relatively short internodes; sheaths 20–30 toothed.
The main stems of assimilating shoots, 100–200 cm high; 10–12 mm in diameter; erect; dirty whitish, with no chlorenchyma; bearing whorls of slender branches at the nodes (these numerous, regular); dying down in autumn. The main stem internodes not swollen; 20–40 grooved; grooves fine, the ribs between them not prominent. 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 (2/3 to 3/4); endodermis comprising a single layer outside the ring of vascular bundles. The main stem sheaths pale, blackish above; about 4 cm long; loose; 20–40 toothed (as many as the grooves). The teeth two ribbed; blackish, subulate; persistent. The primary branching symmetrical. The primary branches numerous; spreading; simple (regular, spreading). The primary branch internodes 4 grooved. The primary branch sheaths 20–30 toothed (the teeth dark). The first branch internodes much shorter than the subtending sheaths. The primary branch internodes solid. Stomata on the sheaths not sunken (the internodes lacking stomata, as well as chlorenchyma).
The cones 4–8 cm long; blunt. Spores released in April.
Distribution. Europe, from Sweden, Denmark and the Black Sea region southwards, Asia Minor and the Caucasus; North Africa; Azores and Madeira; and north-western North America from British Columbia to Ohio. In the British Isles, locally distributed throughout England, Wales and Ireland, absent from north-eastern Scotland; in damp, shady places, ascending to about 400 m.
Classification. Subgenus Equisetum; Section Subvernalia.
Illustrations. • E. telmateia (Sowerby and Johnson). • E. telmateia: stem internode anatomy. • 10 British Equisetum species and hybrids (Sowerby and Johnson).
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’.