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Arenaria serpyllifolia L. s.l., Thyme-leaved Sandwort

Account Summary

Native, rare. Eurosiberian southern-temperate, but widely naturalised beyond its native range.

1901; Praeger, R.Ll.; Co Fermanagh.

January to September.

Growth form and preferred habitats

The favourite habitat in Fermanagh for this apparently rare, but quite insignificant-looking and therefore possibly somewhat overlooked winter- or more rarely summer-annual is in the open, dry, almost bare or thinly vegetated central strip in gravel tracks in coniferous forestry plantations. Here it is associated with other small plants including mosses, Arabis hirsuta (Hairy Rock-cress), Eriophila verna (Common Whitlowgrass) and Catapodium rigidum (Fern-grass). A. serpyllifolia is a pioneer colonist of dry, shallow, warm, mainly neutral to calcareous open, lightly disturbed, unproductive bare stony or sandy soils. Usually it occurs in limestone terrain, although elsewhere in parts of England it is known to tolerate a more acidic reaction, down to nearly pH 5.0 (Grime et al. 1988, 2007).

Germination, growth and reproductive cycle

Being chiefly a winter-annual, most germination occurs in damp conditions in the autumn, the species then overwintering as a seedling or a small plant. A proportion of seed each year remains dormant and becomes incorporated in the soil where it can survive for several years, perhaps up to 30 (Salisbury 1964). Growth of the plantlet resumes in the spring, producing a loose, sprawling and spreading plant up to 25 cm in height. Flowering takes place as late as May and continues into August. The small, five-petalled, star-like flowers are mainly self-pollinated and self-fertilised, although small insects may also visit them for pollen. Seed is set and shed from capsules that split to release them from July onwards. Although there is no obvious dispersal mechanism, the small, light seed appears to be highly mobile (most probably carried by wind), since it occupies a wide range of habitats over a large proportion of the country, and it can also be found growing several metres above the ground on the tops of walls (Ridley 1930, p.29).

Fermanagh occurrence

Locally, the species is rare, there being only ten records of A. serpyllifolia in the Fermanagh Flora Database scattered over nine tetrads. It is ± confined to disturbed limestone terrain lying west of Lough Erne. The author is confident that the survey records reflect both the insignificant appearance and the genuine local rarity of this species, since most of the finds have been by RHN.

Apart from the first record already given above, the details are: railway line at Belcoo (now dismantled), Lower Lough Macnean, 1947, MCM & D; Corraslough Point, Upper Lough Erne, 23 June 1986, RHN & RSF; Lough Nagor, Belmore Mountain, 22 September 1990, RHN; Laghtmacdonnell, 1 km NW of Lough Formal, Big Dog Forest, 23 August 1992, RHN; forest track, Tullinwonny, NE of Lough Formal, 23 August 1992, RHN; on gravel roadsides, Killydrum, near Noon's Cave, 4 January 1993, RHN; track at Ballintempo Forest, 28 August 1993, RHN; Brougher Mountain, 24 April 2000, RHN & HJN; Meenloughabank, 29 May 2009, RHN & HJN.

Variation

A. serpyllifolia s.l. or agg. is now known to contain three taxa, either separate subspecies or occasionally regarded as distinct species. The first two of these are subsp. serpyllifolia and subsp. lloydii (Jord.) Bonnier (subsp. macrocarpa F.H. Perring & P.D. Sell var. lloydii (Jord.) Gutermann & Mennema). Subsp. lloydii is a coastal dune ecotype, confined to shores. The third taxon that previously was named A. serpyllifolia subsp. leptoclados (Rchb.) Nyman, is now given specific status as A. leptocladus (Rchb.) Guss (Stace 2010). These three taxa differ mainly in the size of the plant and in the shape of the fruit capsule.

Irish occurrence

Although this species (in the broad sense, A. serpyllifolia) is widespread in the RoI, especially SE of a line on the map linking Dundalk, Limerick and Cork, in contrast the majority of N Irish records are coastal, from sand dunes, cliffs and walls (New Atlas).

British occurrence

A. serpyllifolia occupies a much wider range of habitats and is very much more widespread in Britain than it is in Ireland. It occurs as a pioneer colonist on bare, open dry ground in areas of basic rocks including serpentine in situations that range from upland screes, summits and cliffs to lowland quarries, mine spoil heaps, railway ballast, waysides and margins of arable fields (Grime et al. 1988, 2007; P.S. Lusby, in: Preston et al. 2002). In distribution, it is very frequent in lowland situations throughout the country, but while it reaches the coast in the far N of Scotland, it is chiefly and most commonly recorded in the Midlands and SE of England (New Atlas). This distribution is probably explained by the preference the species shows for sunny, dry, south-facing rocky slopes on neutral to calcareous soils (Sinker et al. 1985; Grime et al. 1988, 2007).

European and world occurrence

The native distribution of A. serpyllifolia in the broad sense is centred on middle latitudes of Europe and Western Asia (Eurosiberian southern-temperate), but it also extends to NW Africa and the Canaries. In Switzerland, A. serpyllifolia ascends to become part of the subalpine flora. The species has been introduced into northernmost Europe and temperate areas of E Asia, N & S America, Australia, New Zealand and the Philippines. The present world distribution is thus discontinuously circumpolar (Hultén & Fries 1986).

Names

The genus name 'Arenaria' is derived from the Latin 'arena', meaning 'sand', indicating the plant's preference for sandy places (Johnson & Smith 1946). The Latin author Virgil gave the name 'Serpyllus' to the plant we today call Thymus polytrichus (Wild Thyme), and the Latin species epithet 'serpyllifolia' means 'thyme-leaved', meaning with leaves like thyme (Gledhill1985). Hence we have the English common name 'Thyme-leaved Sandwort', which is a perfect example of a so-called 'book name'. Additional English common names include 'Sandweed', another book name variant of 'Sandwort', applied to all members of the genus Arenaria. 'Chickweed' is a name applied to various small plants of similar habit, including annual forms of Veronica, Stellaria and Arenaria, all of which fit into the category of plants that, "chickens and birds love to pick the seed thereof." (Coles 1656, quoted in Britten & Holland 1886 p. 101).

Threats

None.