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Equisetum variegatum Schleich. ex F. Weber & D. Mohr,
Variegated Horsetail

Account Summary

Native, scarce and local. Circumpolar boreo-arctic montane.

1939; Praeger, R.Ll.; Spectacle Lough, Dresternan Td.

March to December.

Growth form and preferred habitats

Fertile and sterile stems of Variegated Horsetail are identical except for the presence or absence of the small, pointed terminal cone which sheds spores in July and August. When taken together, the very slender, generally unbranched, often prostrate, evergreen stems of E. variegatum and the white teeth on the nodal sheaths, which Page so aptly describes as looking like "a broad gothic arch" (Page 1997), clearly distinguish the species from the hybrid it forms with E. hyemale (Rough Horsetail), E. × trachyodon (Mackay's Horsetail).

Variegated Horsetail is a scarce and local, rather variable calcicole species, which in Britain & Ireland occurs in a remarkably wide variety of more or less open, damp to wet, base-rich or calcareous sites, often by running water, or where there is movement of groundwater, even if only at subsoil level. Once established, its rhizomatous growth enables it to form large, compact stands as it still does at Praeger's original fen site at Spectacle Lough, the first Fermanagh site on record. However, it can also be found as scattered individual shoots at some of its more obviously flushed sites, both lowland and at higher elevations. Variegated Horsetail colonises seasonally flooded depressions and damp hollows in several disused quarries in Fermanagh, and it also occurs in similar ground under a hedge in the townland of Clontelaghan near Kinawley.

In other parts of Britain & Ireland, E. variegatum is reported in periodically flooded coastal sand dune slacks and from mountain ledges, neither of which it occupies in Fermanagh (Stewart et al. 1994). As is the case with E. hyemale (Rough Horsetail), in the more northern part of its range, E. variegatum occupies a much wider range of habitats, becoming more or less indifferent to base-status and lime, and being found in much drier situations. In Iceland, for instance, it grows on dry scree slopes and in dry heath (Jonsell et al. 2000).

Fermanagh occurrence

In Fermanagh, E. variegatum has been recorded in a total of 21 tetrads, three of which have pre-1975 records only. It is the eighth most frequent horsetail in the VC. As the tetrad distribution map indicates, the majority of sites are around Lower Lough Erne or on the higher ground to the SW of it.

Irish occurrence

Compared with the five other VCs in N Ireland, Fermanagh undoubtedly has the greater representation of this species. Tyrone (H36) also has three inland sites for Variegated Horsetail (McNeill 2010), but the species is completely absent from Co Armagh (H37) and most of the few remaining N Ireland sites are coastal (NI Vascular Plant Database 2010).

Elsewhere in Ireland, E. variegatum is thinly scattered, occasional to rare down the E coast and across the Midlands (Jermy et al. 1978; Webb et al. 1996).

Variation

Reflecting the wide variety of quite different habitats E. variegatum occupies in these islands, a number of ecotypes have evolved within it. These differ from one another in morphology (ie form, appearance and size), ecology (ie habitat and related features of growth) and in their geographical distribution. Having said this, in some cases ecotype ranges overlap to a degree not yet properly understood. Since ecotypes maintain their distinctive forms when grown together under identical garden conditions, the differences they display must be genetically determined, a feature unique amongst horsetail species in Britain & Ireland (Page 1997).

The most widespread Irish ecotype is var. majus, which as the name suggests is larger than the most typical form found throughout much of Britain, var. variegatum. Var. majus grows erect, rather than decumbent (ie leaning over or lying down, at least in part), and it is generally somewhere between 20 and 80 cm tall, with stems about 3 or 4 mm in diameter, making it half as thick again, or up to twice the width of var. variegatum (Webb et al. 1996; Page 1997).

The existence of these ecotypes undoubtedly provides a useful categorisation and description of the variation within the species (Page 1997). They include a coastal sand-dune form, var. arenarium, common enough elsewhere in Britain & Ireland, but only of incidental interest to us since Fermanagh has no coastline. Another Irish form, but remote from Fermanagh, is var. wilsoni, which is confined to Co Kerry (H1 & H2).

At the same time, it is important to recognise that E. variegatum is a phenotypically very plastic species, each ecotype being capable of displaying considerable modification of form and scale with respect to levels of a wide range of common local environmental variables (Stark 1991). Environmental variables include, for instance, shade, exposure, moisture, competition from other plants, trampling and grazing pressure.

Similar observations of a more local nature can be drawn from Paul Hackney's comparative study of E. variegatum at four sites in N Ireland. Three of the selected sites were coastal sand dunes, but the fourth was the fen shore of Carrick Lake in Fermanagh. Here, Hackney found that the Variegated Horsetail occupied ground with a 90% cover of mosses. It was typically robust, growing up to 50 cm tall, but where the vegetation had been subjected to grazing pressure, the plants only reached 20 cm in height (Hackney 1981). Hackney did not attempt to recognise E. varietatum ecotypes and, since in most of our survey we used the 1977 edition of Webb's An Irish Flora as our field guide, we have not done so either.

British occurrence

E. variegatum is a rather scarce plant in Great Britain, mainly concentrated in the N and W, becoming very rare in the C and S of England (Stewart et al. 1994; Stace 1997). The number of pre-1930 or pre-1970 hectads from which the plant has no recent records suggests the species is in decline and maps indicate that this is happening throughout both Britain and Ireland (Preston et al. 2002). Clearly this is a matter for concern.

European and world occurrence

In terms of geographical distribution, Variegated Horsetail is described as a northern-montane species (Stewart et al. 1994) or a circumpolar boreo-arctic montane species (Preston & Hill 1997). The latter may appear somewhat long-winded but it does summarise a range which stretches in Europe from Iceland and the Arctic Isles, to the northern tip of Scandinavia, thinning markedly towards the S of both Norway and Sweden, and present only at the northern tip of Denmark. In southern areas of these three Scandinavian countries it is also present as an introduction (Jonsell et al. 2000, Map on p. 25). E. variegatum then extends southwards in a somewhat scattered manner until it reaches a further centre of distribution in the Pyrenees, the Alps and other C European mountains (Jalas & Suominen 1972, Map 32).

Further east, E. variegatum reaches the Altai Mountains of C Asia, Manchuria and Japan. In N America, it stretches from the S Rocky Mountains to Labrador and around much of Greenland's coast (Hultén 1962, Map 45; Jonsell et al. 2000). Along the NW Pacific States of N America, the species is represented by a different form, E. variegatum subsp. alaskanum (A.A. Eaton) Hultén.

Names

The Latin specific epithet 'variegatum', means 'irregularily coloured' (Gledhill 1985), and the reference to the black and white banded sheath on the slender green stem is obvious. The English common name is a simple book name translation requiring no comment. As the plant is rare or scarce and it is easily overlooked, it has not accumulated any English folk names.

Threats

A number of sites are vulnerable to changes in agricultural practices. Locally, one quarry site was destroyed when the ground was covered in concrete.