U18 - Cryptogramma Crispa-Athyrium Distentifolium Snow-Bed

Summary

Synonymy

Cryptogrammeto-Athyrietum chionophilum McVean & Ratcliffe 1962.

Constant species

Alchemilla alpina, Athyrium distentifolium, Cryptogramma crispa, Deschampsia cespitosa, D. flexuosa, Galium saxatile, Rumex acetosa, Saxifraga stellaris, Viola palustris, Barbilophozia floerkii, Hylocomium splendens, Hypnum callichroum, Kiaeria starkei, Polytrichum alpinum, Rhytidiadelphus loreus, Cladonia bellidiflora.

Rare species

Athyrium distentifolium, Kiaeria starkei, Polytrichum sexangulare.

Physiognomy

The rare Arctic-Alpine fern, Athyrium distentifolium, occurs occasionally in some other vegetation types of snow-bound montane slopes, but it is most characteristic of this community, sometimes dominant in the field layer as small groups of densely-packed crowns distributed over the rocky ground that is the typical substrate here, or more patchily abundant over extensive areas. The fronds appear after the spring snow-melt, uncurling erect and moderately tall from the shuttlecock bunches, and they die down rapidly in autumn, although the herbage decays only slowly, the patches of red-brown often providing a clear marker of stands when the ground is exposed the following season. Very locally, on higher slopes, plants with smaller fronds and elbowed stipes, giving a strikingly spreading habit, have sometimes been distinguished as A. flexile (e.g. Page 1982). This seems to breed true, though it remains a taxon of doubtful status, perhaps a monstrous variant of A. distentifolium that has gained a firm hold in a few stations (Tutin et al. 1964).

Cryptogramma crispa is the other important plant of the community, quite often more abundant than A. distentifolium, particularly towards lower altitudes where it continues as a major pioneer on drier, more exposed screes than are usual here, and bigger clumps of this species can be very conspicuous in summer with their fresh green foliage. Other ferns are occasionally found, though not usually in any abundance: Thelypteris phegopteris, T. limbosperma, Gymnocarpium dryopteris, Blechnum spicant and Dryopteris dilatata have all been recorded as scattered individuals, and at lower altitudes there is a small overlap with the range of Athyrium filix-femina, a plant with pinnae usually less ascending than in A. distentifolium, and with a distinct indusium over the sorus.

Other vascular constants are Deschampsia cespitosa and D. flexuosa, which usually occur as scattered tussocks, Alchemilla alpina, Galium saxatile, Saxifraga stellaris, Rumex acetosa and Viola palustris. Also very common are Omalotheca supina, Nardus stricta and Oxalis acetosella with occasional plants of Cerastium fontanum, Agrostis capillaris, Huperzia selago, Anthoxanthum odoratum and the Arctic-Alpines Carex bigelowii, Epilobium anagallidifolium, Juncus trifidus, Sibbaldia procumbens and Luzula spicata.