Equisetum sylvaticum L., Wood Horsetail

Account Summary

Growth form and preferred habitats

The only horsetail with branched lateral branches, this feature, together with the graceful, fine textured, drooping, pale yellow-green stems and branches makes Wood Horsetail quite unmistakable and the most beautiful of our horsetails. Sterile and fertile stems are similarly green and branched, the latter differing only in that in May each year they bear a terminal, narrowly oval cone, about 10-20 mm long.

E. sylvaticum is a small to medium-sized, deciduous, colony-forming, rhizomatous horsetail of moderately wet, usually deep, acid to neutral, clay or peaty soils, which, since the species is calcicole, must be more or less constantly flushed with moderately calcium- or base-rich groundwater. In its preference for half-shade and the root-flushing requirement, Wood Horsetail, at its lowland sites at least, is rather similar in its ecological demands to E. telmateia (Great Horsetail) and, to a lesser extent, E. palustre (Marsh Horsetail), with both of which it frequently associates. The roots of both E. sylvaticum and E. telmateia have an absolute requirement for some degree of water movement, while E. palustre can tolerate almost no flow (Sinker et al. 1985; Page 1997).

While Wood Horsetail tends to be most prevalent in damp, sheltered, at least partially shaded sites with constant high humidity (for instance, in fen-carr, woodland margins, glades, hedgerow-, river-, stream- or ditch-banks), it can frequently be found in very much more open and exposed upland positions. In Fermanagh, examples of the latter habitat occur on the Drumbad Scarps, Poulaphouca cliffs and Topped Mountain. In these more exposed sites, as might be expected, it is both rather dwarfed and much more sparsely branched, which makes it quite difficult to recognise (eg see illustration in Page 1997, p. 470).

In Fermanagh, near the NW coast of Ireland, E. sylvaticum can also be found in open, more sunny conditions, as well as in more typical semi-shade. Open habitats here include stabilised scree, quarries, flushed heath and moorland, cut-over bog and even in churchyards. The important essential proviso is that sufficient moisture and the nutrient requirements of the species must be met. The upland tendency of E. sylvaticum on damp, peaty heath and moorland, as well as on cliffs and more sheltered gullies and stream-sides, together with its known woodland shade preferences, suggests the possibility that the upland plants of this horsetail might be relicts of former forest in these sites (Jermy et al. 1978). As with several pteridophytes of moist western heathland, Wood Horsetail appears to have swapped the shade, shelter and constant high humidity under woodland canopy, for an overall heathland region 'Atlantic' climate of overcast, grey, cloudy skies and regular, almost daily, precipitation, evenly spread throughout the year (Gimingham 1972, pp. 11-13; Page 1988, p. 288).

Fermanagh occurrence

E. sylvaticum is the fifth most frequent horsetail in the Fermanagh Flora Database, being represented in 147 tetrads, 27.8% of those in the VC. Eight tetrads contain pre-1976 records only, suggesting some loss of habitat. As the tetrad distribution map indicates, Wood Horsetail is very widespread, but especially frequent on the western limestones. Typical local habitats are wet woods, shaded meadows, flushed heath and moorland slopes, cliffs, streamside banks, damp, shaded ditches and roadsides.

British and Irish occurrence

In Britain, E. sylvaticum is common and widespread in the N & W, but decidedly rare in most areas of C, E and SW England (New Atlas). There has also been a marked decline in the species in lowland England and Wales, which has been going on since before the first BSBI Plant Atlas (Perring & Walters 1962) and continues to the present (C.Dixon & T.D. Dimes In: Preston et al. 2002).

In Ireland, Wood Horsetail is frequent and widespread in the north, but it is much more widely scattered and only occasional in the southern half of the island (Jermy et al. 1978; An Irish Flora 1996; New Atlas).

European and world occurrence

The north-western trend in the British & Irish distribution is mirrored in the horsetail’s European occurrence, covering almost the whole of N and C Europe south to N Spain, the Alps, N Greece, the Balkans and Turkey, but almost entirely absent from the Mediterranean coasts (Jalas & Suominen 1972, Map 36). The species also stretches, sometimes commonly and with very little taxonomic variation, across N Asia to Japan, and it completes its circumpolar range in the higher latitudes of N America, from Alaska to Labrador and on to W Greenland, Iceland and the Faeroes (Hultén 1962, Map 86; Hultén & Fries 1986, Map 17).

Names

Despite its very distinctive and beautiful appearance, E. sylvaticum has not in the past been recognised by most people as anything other than simply another horsetail and for English Common names it has really only got what we refer to as 'book names', such as 'Wood Horsetail' and 'Bottle-brush'. The latter name it shares with E. arvense and also with Hippuris vulgaris (Mare’s-tail) (Britten & Holland 1886). The Latin specific epithet 'sylvaticum' simply gives us the same information as the English common name, meaning 'of woodland' (Gilbert-Carter 1964).

Threats

None.

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