Synonymy

Teesdalio-Arnoseridetum minimae (Malcuit 1929 R.Tx. (1937) 1950 sensu Silverside 1977

Constant species

Aphanes microcarpa, Poa annua, Rumex acetosella, Viola arvensis.

Rare species

Anthoxanthum aristatum, Briza minor.

Physiognomy

Both Viola arvensis and Aphanes microcarpa are constants in the open annual vegetation of the Viola-Aphanes community, although Poa annua often contributes much of the cover by early summer. The diminutive perennial herb Rumex acetosella is very frequent too, producing its annual tufts of shoots in the gaps among the other plants.

Frequent associates, usually at low cover, include Matricaria perforata, Stellaria media, Veronica arvensis and Polygonum aviculare with Bilderdykia convolvulus, Trifolium dubium, Spergula arvensis, Ornithopus perpusillus, Viola tricolor, Chrysanthemum segetum, Alopecurus myosuroides, Scleranthus annuus and Anagallis arvensis among the more common occasionals. This community also provides a locus for the introduced grass, Anthoxanthum aristatum, originally from the Mediterranean and spreading widely in southern England in the nineteenth century but now extremely rare (Salisbury 1964, Perring & Farrell (1977). Briza minor, another national rarity, has also been recorded here but it is more usually found now in other communities.

Areas of bare ground can have scattered plants of acrocarpous mosses such as Bryum microerythrocarpum, B. rubens, Dicranella staphylina, Ceratodon purpureus, Phascum cuspidatum and Pleuridium subulatum.

Habitat

The Viola-Aphanes community is typically found among arable crops on impoverished base-poor sandy soils in the more Continental eastern parts of Britain. The local occurrence of suitable soils and the prevalence of intensive cereal production make this a very scarce vegetation type now.

Synonymy

Stachys arvensis community Silverside 1977.

Constant species

Anagallis arvensis, Poa annua, Polygonum aviculare, Stachys arvensis.

Rare species

Fumaria bastardii.

Physiognomy

The constancy of Stachys arvensis is the most striking feature of the Poa annua-Stachys community, along with P. annua, Polygonum aviculare and Anagallis arvensis. Also very common throughout the assemblage are Spergula arvensis, Stellaria media, Plantago major, Matricaria perforata, Chamomilla suaveolens, Ranunculus repens, Elymus repens and Agrostis stolonifera. Occasionals include Capsella bursa-pastoris, Bilderdykia convolvulus, Fumaria muralis ssp. boraei, Senecio vulgaris, Taraxacum officinale agg., Trifolium repens, Holcus lanatus and Lolium perenne. The total cover of vascular plants is usually high and some stands have a distinctly grassy appearance. In one sub-community, acrocarpous mosses can be varied and quite abundant.

Sub-communities

Chenopodium album-Euphorbia helioscopa sub-community. Chamomilla suaveolens, Sonchus asper and Veronica persica show somewhat higher frequency than usual here but more striking preferential are Chenopodium album and Euphorbia helioscopa. Knotweeds are quite often prominent with Polygonum lapathifolium, P. nodosum and P. persicaria occasionally joining P. aviculare, and Viola arvensis, Atriplex patula, Sinapis arvensis, Sonchus arvensis, Sherardia arvensis and Agrostis capillaris are all preferential at low frequency. Among nationally-scarce plants, this sub-community occasionally provides a locus for Kickxia elatine and Misopates orontium.

Cerastium fontanum-Bryum rubens sub-community. Polygonum persicaria increases in frequency in his subcommunity but more exclusive preferentials are Cerastium fontanum and a variety of acrocarpous mosses of which Bryum rubens, Pottia truncata and Dicranella staphylina are the most common with B. klinggraeffii and B. violaceum less frequent.

Constant species

Anagallis arvensis, Medicago lupulina, Papaver rhoeas, Poa annua, Polygonum aviculare, Veronica persica, Viola arvensis.

Rare species

Veronica triphyllos.

Physiognomy

The Papaveretum argemones comprises annual weed vegetation in which the most striking feature is the abundance of various species of red poppy. Papaver rhoeas is the most frequent and usually the most abundant of these, its bright scarlet flowers appearing from mid-June and continuing intermittently until October, but also common, particularly in the south and east of Britain and beginning to flower earlier, is P. argemone. A third species, like P. argemone in its smaller and paler scarlet flowers, though more widespread, is P. dubium.

Other frequent contributors to the more or less open cover of this vegetation are Viola arvensis, Veronica persica, V. arvensis, Anagallis arvensis, Poa annua, Medicago lupulina, Polygonum aviculare, Bilderdykia convolvulus, Capsella bursa-pastoris and Trifolium repens. Elymus repens and Agrostis stolonifera are common, too, and can be locally abundant.

Occasional in the Papaveretum include Arenaria serpyllifolia (with some plants distinguished as ssp. leptoclados), Galium aparine, Myosotis arvensis, Chenopodium album, Matricaria perforata, Chamomilla suaveolens, Sonchus asper, S. oleraceus and Senecio vulgaris. The nationally rare Veronica triphyllos has also been recorded in this vegetation.

Habitat

The Papaveretum is characteristic of disturbed, light and friable soils that are not too calcareous, throughout the warmer and drier lowlands of Britain and it is especially frequent in cereal fields that have escaped herbicide treatment.

Constant species

Arrhenatherum elatius, Festuca rubralovina, Geranium robertianum, Gymnocarpium robertianum, Teucrium scorodonia, Ctenidium molluscum.

Physiognomy

The Gymnocarpietum robertiani comprises more or less open stands of fern- and grass-dominated vegetation disposed over the distinctive topography of limestone screes and pavement. Scattered fronds of Gymnocarpium, arising separately from the creeping rhizomes, begin to emerge rapidly in late spring, their rather stately forms attaining up to 40 cm or so in height. Among these, occasionally in some abundance, are loose tussocks of Arrhenatherum and, less commonly, Festuca ovinalrubra (not distinguished in available data) and Brachypodium sylvaticum. In sunnier situations, which the fern seems to tolerate well, perhaps because of its somewhat mealy surface (Page 1982), the Brachypodium often has a rather lurid yellow-green tinge. Sesleria albicans does not appear in the table because samples of the community were not collected within the range of this grass but it can figure prominently in this vegetation in the Yorkshire Dales and southern part of the Lake District.

Other very frequent components are Geranium robertianum, commonly showing a reddish hue to its stems with the typically impoverished nature of the substrate, Teucrium scorodonia, Mycelis muralis and Mercurialis perennis. Where clonal patches of the last plant thicken up, the Gymnocarpium seems to suffer and be gradually eclipsed (Page 1982). Less common vascular associates include Origanum vulgare, Carex flacca, Viola riviniana, Senecio jacobaea, Oxalis acetosella, Arabis hirsuta and, in the northern Pennines, Galium sterneri.

Synonymy

Elymetum repentis maritimum, Elymus repens, Potentilla anserina-Elymus repens-Vicia and Elymus repens-Potentilla anserina soziations? Nordhagen 1940.

Constant species

Agrostis stolonifera, Atriplex prostrata, Elymus repens, Festuca rubra.

Rare species

Allium scorodoprasum, Hordeum marinum.

Physiognomy

The Elymetum repentis has a closed grassy sward up to about 1 m tall, generally dominated by Elymus repens with usually smaller amounts of Festuca rubra and Agrostis stolonifera and, beneath, scattered plants of Atriplex prostrata and an open ground cover of Potentilla anserina. Oenanthe lachenalii, Sonchus arvensis, Rumex crispus and Cirsium arvense are occasional and often give a scruffy appearance to the vegetation and tussocks of Juncus gerardii or Festuca arundinacea may be locally prominent. The community is generally richer and more varied than the Atriplici-Elymetum with a wide range of occasionals of low frequency, some characteristic of other disturbed upper-marsh vegetation of strand-lines and reclamation banks, others more typical of rank inland grasslands. Allium scorodoprasum has been recorded in vegetation of this kind on the north Solway coast and Hordeum marinum from Somerset. Bryophytes occur occasionally with Eurhynchium praelongum, Amblystegium riparium, Funaria hygrometrica, Pottia heimii and Bryum spp.

Habitat

The community is characteristic of similar situations to those occupied by the Atriplici-Elymetum: upper-marsh areas where there is often a combination of disturbance, drift-litter deposition and some freshwater influence. It is, however, less consistently confined to well-drained sites, occasionally growing on heavy waterlogged clays.

Synonymy

Suaedetum fruticosae Tansley 1939 p.p.; Agropyro-Suaedetum fruticosae Adam 1976; Halimiono-Suaedetum fruticosae Adam 1976.

Constant species

Halimione portulacoides, Suaeda vera.

Rare species

Arthrocnemum perenne, Suaeda vera.

Physiognomy

The Elymo pycnanthi-Suaedetum verae is of variable appearance. The two association constants are sometimes co-dominant as a more or less closed shrubby cover; in other cases they occur as scattered bushes in a grassy ground. The S. vera shoots provide a niche for a varied flora of epiphytic lichens (Ellis 1960).

Sub-communities

Elymus pycnanthus sub-community: Elymo pycnanthi-Suaedetum verae typicum Géhu & Delzenne 1975; Agropyro-Suaedetum fruticosae Adam 1976. Here the cover of H. portulacoides is low and the vegetation is dominated by complementary proportions of S. vera bushes and stiff clumps of Elymus pycnanthus with usually a little Festuca rubra. The upper edge of stands may be marked in spring by a narrow band of winter annuals such as Cochlearia danica, Myosotis ramosissima, Sagina maritima and Valerianella locusta germinating on drift debris.

Halimione portulacoides sub-community: Elymo pycnanthi-Suaedetum verae halimionetosum Géhu & Delzenne 1975; Halimiono-Suaedetum fruticosae Adam 1976. S. vera and H. portulacoides are co-dominant as a shrubby canopy of variable height over a ground of scattered Puccinellia maritima and Limonium cf. vulgare, often with a little Aster tripolium, annual Salicornia spp., Spergularia media and Suaeda maritima. The sub-community provides an occasional high-level context for Bostrychia scorpioides and Pelvetia canaliculata.

Synonymy

Spergulo-Chrysanthemetum (Br.-Bl. de Leeuw 1936) R.Tx. 1937 sensu Silverside 1911 p.p.; Medicagi-Ranunculetum parviflori Silverside 1977 p.p.

Constant species

Anagallis arvensis, Cerastium glomeratum, Fumaria muralis ssp. boraei, Juncus bufonius, Poa annua, Senecio vulgaris, Sonchus asper.

Rare species

Allium babingtonii, Briza minor, Fumaria bastardii, Silene gallica.

Physiognomy

The Cerastium glomeratum-Fumaria muralis ssp. boraei community is one of the British weed assemblages in which fumitories figure with some prominence. F. muralis ssp. boraei is the most common taxon here and it can be abundant. Less frequent in the community, though locally prominent, are F. officinalis (a plant with a wider distribution nationally than F. muralis ssp. boraei), and the nationally scarce F. bastardii and F. occidentalis.

Other distinctive constants of this kind of vegetation are Cerastium glomeratum and Juncus bufonius with Anagallis arvensis, Poa annua, Senecio vulgaris and Sonchus asper. P. trivialis and Coronopus didymus are among the frequent associates but more striking is the common occurrence of Chrysanthemum segetum and the nationally rare or scarce Ranunculus parviflorus, Briza minor and Silene gallica. Gladiolus byzantinus is a common escape from the bulb crops among which this assemblage is often found.

Occasionals include Veronica persica, Medicago arabica and Rumex acetosella with the South African introduction Oxalis pes-caprae naturalised here, though with varying frequency in the different sub-communities, and another introduced sorrel O. corniculata occurring much more rarely.

Synonymy

Lythrum hyssopifolia stands Preston & Whitehouse 1986.

Constant species

Anagallis arvensis, Juncus bufonius, Lythrum hyssopifolia, Matricaria perforata, Plantago major, Polygonum aviculare, Polygonum persicaria, Bryum klinggraeffii, Pottia starkeana ssp. minutula, Riccia glauca.

Rare species

Lythrum hyssopifolia.

Physiognomy

The Lythrum hyssopifolia-Juncus bufonis community comprises ephemeral vegetation which, by mid-summer, is typically dominated by mixtures of the nationally rare Lythrum hyssopifolia, together with Juncus bufonius, Plantago major (diagnosed as ssp. intermedia by Preston & Whitehouse 1986), Polygonum persicaria and P. aviculare. Also frequent throughout among the vascular associates are Mentha arvensis, Rumex crispus and seedlings of Salix spp. Elymus repens is occasional and, in sites which have been undisturbed by recent ploughing, Polygonum amphibium tends to increase. Bryophytes are an important element in the vegetation with Bryum kling graeffii and Riccia glauca common throughout, the former with modest abundance.

Preston & Whitehouse (1986) noted a consistent, but overlapping, contrast between the stands they sampled but not sufficiently sharp to characterise sub-communities. To one extreme, species such as Anagallis arvensis, Alopecurus myosuroides, Kickxia elatine, K. spuria and more obviously Anthemis cotula and Aethusa cynapium ssp. agrestis, tended to be associated with Pottia starkeana ssp. minutula, Barbula unguiculata, B. argenteum, Dicranella staphylina and D. varia. To the other, Matricaria perforata and Equisetum arvense were found with Physcomitrella patens, Riccia cavernosa, R. subbifurca and Pohlia carnea.

Constant species

Several distinct taxa can be recognised among the British annual Salicornias but diagnosis below the level of the three groups S. europaea, S. procumbens and S. pusilla is difficult for non-specialists. Here, all annual taxa encountered are described under Salicornia agg. and this is the sole constant of the community.

Rare species

Arthrocnemum perenne.

Physiognomy

The community comprises ephemeral stands of annual Salicornias sometimes with no other species. The vegetation is invariably somewhat open and though Salicornia agg. is always conspicuous, the density of plants is variable: around The Wash, for example, Salicornia agg. cover is high whereas at sites with sandier substrates the density can be very low. There is often an algal mat over the substrate surface but vascular companions are usually very few. Scattered plants of Puccinellia maritima, Suaeda maritima and Spartina anglica occur frequently with occasional records for a variety of other lower marsh species. At a few sites (Blakeney Point, for example), Fucus vesiculosus ecad caespitosus is abundant.

Sub-communities

With careful identification of distinct taxa, it may be possible to define a range of communities within this broad general unit as a number of Continental authors have done (see, for example, Géhu & Delzenne 1975). Ball & Tutin (1959) recommend collecting a dozen specimens from populations in September/October when the characteristic colours have developed.

The sampling of weed vegetation and other assemblages of open habitats

In the days before political correctness was an issue, the editors of a renowned book on weeds made the memorable observation that, as a class, weeds had ‘much in common with criminals’: that is, when not engaged in nefarious activities, they were often admirable. Certainly, that book (Salisbury 1964), then and still the most accessible account of these plants, did much to inform and engage, and it grouped weeds into broad ecological categories according to habitat – cornfield and arable weeds, grassland weeds, weeds of sandy soils, of chalk, of roadsides and wastes, and of gardens. This was scarcely a classification, of course, but it was a considerable advance on Tansley (1939) which, like its predecessor (Tansley 1911), made only fleeting references to weed vegetation of any kind, and then usually within the context of successions to other plant communities. In fact, Salisbury himself (1964) was building on previous work, like the survey of Buckman (1856), who described arable weeds of different soil types, and the studies of Brenchley (1911, 1912, 1913), who made more comprehensive field lists in various localities, noting the geology, soils and crops with which the plants were associated.

Synonymy

Dune grassland Gimingham 1964a.

Constant species

Achillea millefolium, Ammophila arenaria, Arrhenatherum elatius, Festuca rubra, Poa pratensis.

Rare species

Acaena novae-zelandiae, Astragalus danicus.

Physiognomy

The Ammophila arenaria-Arrhenatherum elatius grassland includes rank, tussocky swards in which both Festuca rubra and Ammophila remain very common, the former especially being often abundant, indeed the most frequent dominant overall, the latter rather more patchily represented, but plentiful and vigorous in some stands. Compared with other dune grasslands, however, a noticeable difference here is the common occurrence of Arrhenatherum elatius, often growing in some abundance and quite frequently co-dominant. Other grasses figure, too, though their contribution to the cover is generally small. Poa pratensis agg. (probably P. subcaerulea in many cases) is constant in small amounts, for example, and Dactylis glomerata is often found, though only exceptionally with any abundance. More occasionally, there can be some Holcus lanatus, Trisetum flavescens, Elymus pycnanthus, E. farctus and E. repens, but smaller species like Koeleria macrantha, Agrostis capillaris and Anthoxanthum odoratum tend to be very scarce. Carex arenaria is only moderately common, and Luzula campestris rather infrequent.

Quite a variety of dicotyledonous herbs occur in the community, the commonest able to grow up tall through the grasses or form a loose, bushy understorey in more open parts of the sward.

Stands dominated by rayed Aster tripolium have been encountered in situations with some freshwater influence such as brackish ditches behind sea walls where Spartina anglica and Puccinellia maritima are frequent associates. Beeftink (1962, 1965) has described similar vegetation from sites with local freshwater flushing as a distinct Aster tripolium sociatie. Rayed A. tripolium is also abundant on periodically-flooded saline muds in inland salt-marshes with Spergularia marina and Puccinellia distans (see the Puccinellietum distantis asteretosum of Lee 1977; also Edees 1972).

Although some floras note a certain habitat distinction between rayed forms of A. tripolium and the var. discoideus (e.g. Petch & Swann 1968, Jermyn 1974, Gibbons 1975), the situation is far from simple. The var. discoideus can also occur in brackish habitats and Jermy & Crabbe (1978) have recorded vegetation rich in dwarf rayed A. tripolium and Suaeda maritima from Salen Marsh, Mull, where there is little freshwater influence (cf. the intertidal Suaedeto maritimae-Asteretum tripolii Hocquette & Géhu 1965 in Ghestem 1972). Furthermore, even within the rayed form there appears to be a complex of genetically determined variation adapted to different environmental conditions (Gray 1971, 1974; Gray et al. 1979). Further sampling is needed to establish the ecological implications of this variation and to check the validity of erecting separate communities for the different forms.

Constant species

Epilobium angustifolium.

Physiognomy

The Epilobium angustifolium community is overwhelmingly dominated by E. angustifolium, the tall shoots of which can reach well over 1 m by summer. No other species is frequent throughout but the commonest associates overall are Rubus fruticosus agg., Holcus lanatus, Pteridium aquilinum and Urtica dioica with various other species reflecting the different situations in which this kind of vegetation can develop.

Sub-communities

Holcus lanatus-Festuca ovina sub-community. In this grassy or heathy vegetation, E. angustifolium is accompanied by frequent Holcus lanatus and Festuca ovina, occasional Anthoxanthum odoratum, Agrostis capillaris, Potentilla ereeta, Galium saxatile and Teucrium scorodonia, and sometimes by scattered Calluna vulgaris, Erica cinerea, Ulex europaeus and U. gallii and sparse or patchy Pteridium.

Urtica dioica-drsium arvense sub-community. U. dioica is a frequent associate here, though not rivalling E. angustifolium in cover, and there are often scattered individuals of Cirsium arvense and C. vulgare. Holcus lanatus remains common but is occasionally accompanied here by Arrhenatherum elatius, Dactylis glomerata, Holcus mollis, Deschampsia cespitosa and Poa trivialis, with Heracleum sphondylium and Galium aparine. Patches of Rubus fruticosus agg. can sometimes be seen.

Rubus fruticosus agg.-Dryopteris dilatata sub-community. Rubus fruticosus agg. is constant here, along with Dryopteris dilatata, and occasional Pteridium aquilinum and saplings of Betula pendula, B. pubescens, Pinus sylvestris, P. nigra, Quercus robur and Q. petraea. Bryophytes Such as Mnium hornum, Aulacomnium androgynum and Lophocolea bidentata s. l. are sometimes prominent on decaying wood.

Constant species

Lythrum portula, Ranunculus flammula.

Rare species

Alopecurus aequalis, Pilularia globulifera.

Physiognomy

The Lythrum portula-Ranunculus flammula community comprises generally open vegetation in which L. portula and R. flammula are the only constants, the former sometimes occurring with abundance, occasionally in locally monodominant stands. Apart from Eleocharis palustris, other associates are recorded rather sporadically and only rarely with high cover values, but can be quite varied: Agrostis stolonifera, Juncus bufonius, J. effusus, J. articulatus, Galium palustre, Callitriche stagnalis, Littorella uniflora, Mentha aquatica, Alisma plantago-aquatica, Myosotis scorpioides and Apium inundatum have all been found here. The community also provides a locus for the nationally rare Pilularia globulifera, a perennial plant but one quick to colonise the damp open muds characteristic of this vegetation (Jermy in Stewart et al. 1994), Limosella aquatica, an ephemeral herb, and Alopecurus aequalis, an annual grass which invades here as water levels drop (Hubbard 1984, Twist in Stewart et al. 1994).

Habitat

The Lythrum-Ranunculus community is typical of silty or peaty soils, wetted and exposed by fluctuating or temporary waters around pool, lake and reservoir margins and in flooded gravel and brick-earth workings.

Compared with the habitats of Bidention assemblages, the situations colonised by this vegetation are not nutrient-rich and, though the cover of the sward can be extensive, the herbage does not have the lush character of those nitrophilous ephemeral communities.

Synonymy

Obionetum and Halimionetum auct. angl.

Constant species

Halimione portulacoides, Puccinellia maritima.

Rare species

Arthrocnemum perenne, Frankenia laevis, Inula crithmoides, Limonium bellidifolium, Suaeda vera.

Physiognomy

This is a closed, species-poor association in which Halimione portulacoides is constant and physiognomically conspicuous as a bushy canopy up to 50 cm high or as a virtually prostrate carpet. Puccinellia maritima is also constant and there is frequently a little Suaeda maritima and sparse records for a variety of species from both low and upper marsh. Epiphytic algae are often abundant on the lower stems of the H. portulacoides and at some sites small patches of fucoids are present beneath canopy gaps.

Sub-communities

Géhu & Delzenne (1975) allocated samples of Halimione portulacoides vegetation with the red alga Bostrychia scorpioides to the separate association Bostrychio-Halimionetum portulacoidis (Corillion 1953) R.Tx. 1963. Although B. scorpioides was recorded occasionally here, there is no substantial floristic reason for distinguishing samples containing this species as even a sub-community within the Halimionetum. The three following subcommunities are, however, quite distinct.

Sub-community with Halimione portulacoides dominant.

In this most species-poor sub-community, H. portulacoides always has high cover values (usually >90%) and there is usually a sparse undercover of Puccinellia maritima and some Suaeda maritima. The H. portulacoides may be present as a low or tall even-topped canopy or as discrete hemispherical bushes 1–2 m diameter and up to 50 cm high.

Synonymy

Armeria maritima-Aster tripolium provisional nodum Ivimey-Cook & Proctor 1966 p.p.; Crithmum maritimum rock-crevice community Proctor 1975; Crithmion communities Shimwell 1976 ms.

Constant species

Crithmum maritimum, Spergularia rupicola, Festuca rubra, Armeria maritima.

Rare species

Parapholis incurva, Limonium recurvum (and probably other apomicts of the L. binervosum group, e.g. L. paradoxum, L. transwallianum; see also Ingrouille 1981).

Physiognomy

The Crithmo-Spergularietum has a low-growing, very open cover of scattered vascular perennials rooted in rock crevices. The distribution of the plants and the overall appearance of the vegetation are strongly influenced by the nature of the substrate and, in general, none of the association constants can be said to be truly dominant, though all but Spergularia rupicola may be particularly abundant in individual stands. Plantago maritima is the most frequent associate throughout the association. Bryophytes are rarely conspicuous with only Schistidium maritimum and Tortella flavovirens recorded very occasionally. The only lichens are epilithic.

Sub-communities

Typical sub-community: Crithmo-Spergularietum rupicolae typicum Géhu 1964. The four association constants here account for the bulk of the vegetation cover and, of the associates, only Plantago maritima and P. coronopus attain a constancy above I.

Iula crithmoides sub-community: Crithmo-Spergularietum rupicolae plantaginetosum coronopi Géhu 1964 p.p. Spergularia rupicola is rather less frequent in this sub-community but Inula crithmoides and Plantago coronopus are both constant and the former may be abundant. Limonium binervosum (including its apomicts), Parapholis incurva and Desmazeria marina are all preferentially frequent.

Synonymy

Asplenium trichomanes-Fissidens cristatus Association Birks 1913 p.p.

Constant species

Asplenium ruta-muraria, Asplenium trichomanes, Homalothecium sericeum, Porella platyphylla.

Rare species

Hornungia petraea, Silene nutans.

Physiognomy

The Asplenietum trichomano-rutae-murariae comprises generally very open and often fragmentary stands of crevice vegetation in which diminutive ferns and bryophytes are the most distinctive components. The commonest ferns here are Asplenium ruta-muraria and A. trichomanes, the latter almost always the tetraploid ssp. quadrivalens according to Page (1982) although, on Skye, most of the plants examined have proved morphologically intermediate between this and the diploid ssp. trichomanes (Wood 1969). Both A. trichomanes and A. ruta-muraria are more or less evergreen plants whose small rosettes are very frequent here but of low total cover. The bulkier A. adiantum-nigrum occurs very rarely in the community but A. viride is typically absent. Ceterach officinarum is a good preferential but it is only really common in this vegetation towards the south and west of Britain.

Among other perennial vascular plants, only Festuca ovina, Koeleria macrantha, Thymus praecox, Sedum acre and Helianthemum nummularium occur with any frequency, with Arenaria serpyllifolia and Saxifaga tridactylites figuring as ephemerals, but all of these species are strongly preferential to one sub-community which is transitional to rocky turf where the cover of plants is greater. Through the community as a whole, the other prominent element in the vegetation comprises bryophytes whose cushions and mats can cram the crevices and spread out a little way over the rock surfaces.

Synonymy

Carex arenaria community West 1936, 1937; Corynephorus canescens localities Marshall 1967 p.p.; Carex arenaria vegetation Noble 1982 p.p.

Constant species

Carex arenaria.

Rare species

Astragalus danicus, Corynephorus canescens.

Physiognomy

The Carex arenaria community includes very open to more or less closed swards in which the sand-sedge is the most abundant plant, where vascular associates are few in number and usually sparsely distributed and where there is hardly any contribution from mosses or lichens on what is often still a somewhat mobile sand surface. Where the sedge is invading freshly-deposited material, its initial cover may be very low, the shoots emerging, spaced out and generally single, in striking straight lines from the far-creeping rhizomes. If accretion continues at a fairly modest rate, well-established plants can keep pace but, as the sand starts to become stabilised, clones can thicken up very considerably with densely-packed shoots growing tiller-like from short, closely-spaced branches. Up to several hundred shoots per m2 have been recorded in this vegetation, but vigour is affected by soil conditions in a particular stand and by grazing which can reduce the sedge to very squat proportions (Tidmarsh 1939, Noble 1982).

In younger stands, or where C. arenaria has preempted a site and remained strongly dominant, there may be very little else growing among it.