Selaginella selaginoides (L.) P. Beauv., Lesser Clubmoss
Account Summary
Native, occasional. Circumpolar boreal-montane, but rather disjunct in both Eurasia and N America; perhaps better considered mainly arctic-montane.
1882; Stewart, S.A.; Drumbad Scarps, Lough Navar Forest Park.
June to December.
Growth form and preferred habitats
A tiny, delicate, moss-like perennial, Lesser Clubmoss is both montane - found above the notional tree-line in areas dominated by blanket-bog, and in heathland, and also lowland, growing in wet flushed, base-rich ground beside lakes and streams. Being very small and rather inconspicuous it needs to be positively searched for in seepage areas, stream sides and near lakeshores, or in open, exposed habitats. It often occurs in shallow soils where the growth of competing species is limited.
The perennial stems of Lesser Clubmoss are generally extremely inconspicuous, weak-looking, prostrate, branching only occasionally, and they trail over and through mossy vegetation and the stem bases of other, more vigorous vascular plants. Slightly easier to spot are the annual cone shoots, of which one or two are produced per stem during July and August.
Pinguicula vulgaris (Common Butterwort) is almost invariably a good indicator of the likely presence of S. selaginoides and it is interesting to compare the distribution maps of the two species. In late August and early September the pinkish-yellow colour of the senescing erect annual cone shoot of Lesser Clubmoss makes it much easier to observe (provided, that is, if one bends right over and looks closely and diligently in the right sort of habitat!). The small size of the plant and the fact that it has a soft, moss-like texture immediately distinguish S. selaginoides from all other species of clubmoss in Britain and Ireland.
Reproduction
The terminal spore-bearing shoots are shaped like an Indian club, or a fox's tail and are held erect, typically between 2 and 10 cm tall. The actual cone is leafy and ill-defined, bearing both sterile leaves and fertile spore-bearing ones (ie sporophylls), carrying separate spore sacs (ie sporangia). The latter structures contain asexual spores of one of two kinds on separate parts of the fertile branch: either four white relatively large female megaspores per megasporangium, or vast numbers of microscopic yellow male microspores per microsporangium (Jermy & Camus 1991; Page 1997). Sexual reproduction follows on a microscopic prothallus produced by each (or some) of the megaspore(s).
Fermanagh occurrence
This tiny, delicate, moss-like perennial has been recorded in 56 Fermanagh tetrads (10.6% of those in the VC), 46 of them with post-1975 records. It is occasionally found on the shores of Lower Lough Erne, but is quite frequent and widespread on the upland limestones of the Western Plateau. The details of the most outlying stations to the S of the county are: Knockninny, 1900, W.N. Tetley; Kilroosky Lough ASSI, 1980, R.S. Weyl; and moorland at Skeaghoge Td, 1989, RHN.
The nature of base-rich habitats
The one characteristic that links all S. selaginoides habitats is the requirement for soil enrichment and aeration associated with the movement of base-rich water. The base (ie the positively charged cation) most typical of such waters is calcium, but in the Lough Navar area of Fermanagh the parent rock has become partially dolmitized and thus base-rich water here contains both calcium and magnesium (Whitten & Brooks 1972).
In other sites, base-yielding rocks may include various mica-schists, volcanic tuffs, lavas, or basalts, some of which may release minerals in quantities that are toxic to certain plants. Base-rich water is not necessarily nutrient-rich as far as plant growth is concerned, and if it is derived from dissolution of limestone or dolomite it is always nutritionally unbalanced, being oversupplied with Ca++ ions. As ground-water percolates through soil, however, it can accumulate and transport dissolved nitrogen and available phosphate, plus traces of other elements essential for plant development, which might otherwise be scarce or absent in a particular site and thus become limiting for plant growth.
The best concise account of the concept of base-rich soil and plant nutrient status known to the current author appears in Page's book, Ferns. Their habitats in the British and Irish landscape (Page 1988, pp. 70-3 and 311-2), and this is highly recommended reading for anyone who is puzzled by the usage of this technical term. Page clarifies the essential qualifications associated with understanding and applying this rather difficult and potentially (and actually), very woolly ecological concept.
Fossil record
Micro-fossil megaspores of S. selaginoides have been found at Derryvree, near Maguiresbridge in Fermanagh in a full-glacial freshwater deposit of Middle Midlandian age radio-carbon dated to 30,500 BP (Colhoun et al. 1972). The flora and fauna of this fossil deposit indicated open tundra vegetation and a periglacial climate prevailed at the time it was laid down.
Elsewhere in Britain & Ireland, the fossil record for S. selaginoides is well studied, both microspores and megaspores being readily recognised. The sediment studies prove the species has been present in these islands during the last four glacial stages. Lesser Clubmoss has been less frequently recorded during some of the intervening warm interglacial periods. This is not terribly surprising, since it cannot cope with tall, shading vegetation typical of the forest maximum. However, the species has been found as fossils throughout the entire current heavily studied interglacial, which is called the Flandrian in Britain and the Littletonian in Ireland.
British and Irish occurrence
The fossil record also shows that the plant has contracted in range northwards compared to its late glacial distribution (Godwin 1975). Although we do not understand what factor(s) caused this range contraction, it is particularly well demonstrated in the British Isles, where the species until recent historical times occurred north of a line in Britain from Barmouth in Wales to Skegness in Lincolnshire, and in Ireland from Foynes near Limerick, eastwards to Arklow. There is just one exceptional site below this demarcation, which is on the coast near Wexford town (Jermy et al. 1978).
The distribution of S. selaginoides has been seriously affected by drainage and the intensification of agriculture in the last 50 to 70 years, with significant losses in the SE of England before 1930. Approximately 70 additional sites were lost between 1950 and 1990. Over the same period, similar environmental pressures in Ireland have resulted in the loss of around 35 sites of the species throughout the island, but again losses have been particularly concentrated in the south of its range (Jermy et al. 1978; Jermy & Camus 1991).
European and world occurrence
Beyond Britain and Ireland, S. selaginoides has an amphi-atlantic or circumpolar, boreal-montane distribution (Hultén 1958; Hultén & Fries 1986, Map 8; Preston & Hill 1997). In the view of the current author, the absence of records in Siberia and major gaps in Asia in general, does not warrant describing the distribution as circumpolar. The disjunctions are simply too wide. Furthermore, the published European distribution is very definitely disjunct and appears to fit the arctic-alpine (or arctic-montane) pattern better than the more continuous boreal-montane picture (Jalas & Suominen 1972, Map 13). The distribution of S. selaginoides extends quite far south in Finland, the Baltic region and Denmark. Otherwise its distribution closely resembles that of Diphasiastrum alpinum (Alpine Clubmoss) (Jalas & Suominen 1972, compare Maps 12 & 13). Preston & Hill (1997) regard the latter as circumpolar arctic-montane. Most unexpectedly, Page (1971) has discovered a single extremely disjunct outlying station of S. selaginoides lying 2100 km south of its nearest European mainland station, on the Canary Island of Hierro.
Names
The genus name 'Selaginella' is the diminutive of 'Selago', an ancient name applied by the classical Roman, Pliny to a plant resembling Sabina herba, an old name of Juniperus sabina (Gilbert-Carter 1964). The plant Pliny was referring to was a clubmoss, the whole group being then named 'Selago', including the genus we know as 'Lycopodium' together with subsequent splits from it (Johnson & Smith 1946). The specific epithet 'selaginoides' is Latin meaning, 'Selago-like' or 'clubmoss-like', probably meaning, 'like Lycopodium selago', an earlier name for the current species (Gledhill 1985; Stearn 1992). The English common name 'Lesser Clubmoss' is a typical book name, probably of Victorian origin.
Threats
Afforestation of the species' upland habitat, or improvement of rough or damp ground for agricultural purposes.
ISOETACEAE – Quillwort family