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Diphasiastrum alpinum (L.) Holub, Alpine Clubmoss

Account Summary

Native, very rare. Circumpolar arctic-montane.

1 June 1991; Tickner, M.; Altscraghy, Cuilcagh slopes.

Throughout the year.

Growth form and preferred habitats

This moss-like, low-growing, blue-green, arctic-alpine (or alpine-montane) clubmoss grows in short grass over shallow, well-drained, acid peat, often over rocks on or near mountain summits. The slender, wiry, spreading stems produce distinctive, short, erect, evergreen branches clothed with four tightly overlapping ranks of leaves, giving the foliage a rather cypress-like appearance. The shoots fork frequently and evenly to produce clusters of branches all of identical length which often develop in a fan-like, decumbent manner. Fertile branches terminate in a solitary stalkless cone 1-2 cm long, which turns pale yellow as the asexual spores mature and are released in late July and August (Step & Jackson 1945; Page 1997).

Fermanagh occurrence

In Fermanagh, there is just one quite large, sprawling patch growing amongst Sphagnum and Racomitrium moss and spilling down a rock outcrop on the NE face of Cuilcagh mountain, near the summit at an altitude of about 580 m. It was found during a survey of the Cuilcagh Plateau for the Royal Society for the Protection of Birds. A herbarium voucher was deposited in DBN. The site has been revisited several times, most recently in September 2010, when the plant was found in good condition.

Irish occurrence

Elsewhere in Ireland, Alpine Clubmoss is known only from a few scattered localities on the acidic high mountains of Ulster, W Mayo, W Galway, Offaly and Wicklow (Jermy et al. 1978). In Northern Ireland, the two main areas for the species remain the granite Mourne Mountains, Co Down (H38), where in the past it occurred on six different peaks, and the basaltic Garron Plateau, Co Antrim (H39). There are also isolated stations in the Sperrin mountains and on Slieve Gallion in Co Londonderry (H40), plus this recent Fermanagh discovery (Hackney et al. 1992; NI Vascular Plant Database 2002). The lower altitude limit for the NI sites is around 300 m, considerably less than the 457 m given for British mainland sites (Page 1997).

British occurrence

In Great Britain, Alpine Clubmoss has a pronounced northern and western distribution on the higher hills of Scotland, N England and Wales, with outliers in the Derbyshire Pennines, the Worcestershire Malvern hills and possibly also in Devon – although the latter records need confirmation (Jermy & Camus 1991). D. alpinum is characteristic of (and in Wales, at least, can become locally dominant on) well-drained, shallow, peaty slopes, on exposed and/or heavily grazed sites, where plant competition is reduced by these environmental pressures (Page 1997).

Recent changes

Like other clubmoss species, D. alpinum populations and its distribution have undoubtedly suffered a decline in the recent past, particularly at lower altitudes (Jermy et al. 1978; N Ireland Vascular Plant Database 2002). The scale of past losses in Ireland is clearly seen from hectad statistics in the New Fern Atlas (2005), which show the species mapped in a total of 49 squares, only 25 of them with post-1970 records (Wardlaw & Leonard 2005).

Land-use changes, including the extension of coniferous plantation on ever higher ground, and increased livestock stocking densities on upland moorland and heaths has resulted in losses of D. alpinum in both N England and N Ireland, and very probably also in other regions of Britain & Ireland. Like all clubmosses, D. alpinum is very vulnerable to fire. In addition, sulphur dioxide air pollution is undoubtedly responsible for the disappearance of the plant from the hills overlooking Belfast in the late 19th century. Despite the advent of clean air legislation and its enforcement in recent years, this factor continues to operate and it certainly must be responsible for some of the losses recorded in sites downwind of major cities in Britain (Jermy et al. 1978; Page 1997).

European and world occurrence

Beyond Britain & Ireland, D. alpinum has a classic disjunct arctic-alpine distribution in Europe (Jalas & Suominen 1972, Map 12), and it would be circumpolar were it not for a rather unexpected absence from much of the arctic region of central Canada, creating a large gap in the distribution (Hultén & Fries 1986, Map 6).

Uses

In past times, D. alpinum was collected and used as a source of dye mordant in place of the usual chemical fixative, alum. Experiment has shown that plant dyes fixed with mordants from clubmoss species produce softer, more permanent colours than those achievable with alum (Page 1988).

Names

I cannot find a derivation for the genus name 'Diphasiastrum', except that it must in some way connect with a synonym of Lycopodium, 'Diphasium'. The word element 'diphasia' suggests something that exists in, or exhibits 'two stages'.

Threats

Increased sheep density on upland moorland and heaths has resulted in losses of D. alpinum in both N England and N Ireland. Air pollution is an increasing threat in some areas. The solitary nature of the Fermanagh plant renders it vulnerable, but the site is rather difficult of access, reducing the likelihood of it being grazed.