Synonymy

Polytrichetum sexangularis (Rübel 1912) Watson 1925, Br.-Bl. 1926 sensu Birse 1984; Salix herbacea nodum Poore 1955c p.p.; Polytricheto-Dicranetum starkei McVean & Ratcliffe 1962.

Constant species

Deschampsia cespitosa, Kiaeria starkei, Oligotrichum hercynicum, Poly trichum sexangulare.

Rare species

Carex lachenalii, Cerastium cerastoides, Luzula arcuata, Sibbaldiaprocumbens, Conostomum tetragonum, Kiaeria starkei, Pohlia ludwigii, Poly trichum sexangulare, Anthelia juratzkana, Moerckia blyttii, Pleurocladula albescens.

Physiognomy

The Polytrichum sexangulare-Kiaeria starkei snow-bed brings together a variety of bryophyte-dominated vegetation in which the most consistent species are the montane rarities Kiaeria starkei and Polytrichum sexangulare, together with P. alpinum and Oligotrichum hercynicum. K. starkei is usually the most abundant of these and, where snow lies particularly late, its yellowish-green shoots can form a virtually pure carpet, but other mosses and hepatics can be locally dominant. Barbilophozia floerkii, for example, is often quite abundant in the carpet and sometimes exceeds K. starkei in cover, forming extensive dark green patches, and stands rich in K. falcata and the rare Pohlia ludwigii are also occasionally found. Another uncommon bryophyte, Pleurocladula albescens, can occur in some quantity too, the pale colour which gives it its name developing best, according to Watson (1925), where the plants are long deprived of air and light by the snow. Both Racomitrium heterostichum and the rare Conostomum tetragonum can be moderately abundant, though these species are not so consistently important here as in the various Salix-Racomitrium snow-beds.

Other bryophytes which generally contribute to the mat as scattered shoots and small patches include Racomitrium fasciculare, R. lanuginosum, R. canescens, Pohlia drummondii, Nardia scalaris, Lophozia sudetica (perhaps including some L. wenzelii) and, more locally, the rare hepatics Anthelia juratzkana and Moerckia blyttii. Lichens are much less numerous and never abundant, but Cladonia bellidiflora and Cetraria islandica are quite frequent and Solorina crocea is sometimes found.

Vascular plants are typically sparse, although the combination of frequent Deschampsia cespitosa, Carex bigelowii, Omalotheca supina and Saxifraga stellaris is very characteristic of this community, the pure white flowers of the last, emerging through the late-melting snow, being one of the most memorable sights of summer botanising in the Highlands. Huperzia selago, Nardus stricta, Alchemilla alpina, Silene acaulis and Sibbaldia procumbens are also occasional to common, and this kind of vegetation provides one locus for the rarities Cerastium cerastoides, Carex lachenalii and, sometimes straying from more exposed situations, Luzula arcuata.