Synonymy

Tufaceous mounds Holdgate 1955a p.p.; Cratoneuron commutatum-Saxifraga aizoides nodum McVean & Ratcliffe 1962, Birks 1973; Cratoneuron springs Ferreira 1978; Cratoneuron drip-zones Ferreira 1978; Cratoneuron commutatum Community Birse 1980; Cratoneuron filicinum Community Birse 1980.

Constant species

Festuca rubra, Bryum pseudotriquetrum, Cratoneuron commutatum.

Physiognomy

Cratoneuron commutatum occurs frequently and with a measure of local abundance in a variety of calcareous mires, but in the Cratoneuron commutatum-Festuca rubra spring it is consistently dominant in large swelling masses, often forming prominent mounds or banks, of a golden-green colour grading to orange-brown. In some stands, which seem to preserve the same general floristic composition, C. filicinum accompanies or totally replaces it: the two species can show intergradations, and indeed both exhibit wide intraspecific variation (Bell & Lodge 1963, Smith 1978) but, by and large, C. filicinum is a smaller and somewhat stiffer plant and its stem leaves are plicate.

Other bryophytes can make a contribution to the mat, though typically it is a minor one. However, Bryum pseudo triquetrum is very common and occasional include Philonotis fontana and the distinctly calcicolous P. calcarea, Aneura pinguis, Pellia endiviifolia, Drepanocladus revolvens, Gymnostomum recurvirostrum, G. aeruginosum, Brachythecium rivulare and Dicranella palustris. Very typically, there is some tufa deposition among the bryophyte shoots, which lends the mat a distinctive crunchy texture and allows it to build up into mounds.

The vascular element of the vegetation is typically species-poor and of low total cover with, in many stands, just a few scattered herbs. But there is consider able variation in this associated flora from place to place and, particularly where stands are developed over gently-sloping ground, a richer and more extensive herb layer can be found, such that the vegetation comes close to the Cratoneuron-Carex spring or to a Caricion davallianae flush. Often, however, the only species present are Festuca rubra, Cardamine pratensis and Saxifraga aizoides. The last can be quite conspicuous here, particularly when it has its yellow summer flowers, but it is generally present only in small amounts and is totally absent from springs of this kind throughout southern Scotland (e.g. Meek 1976, Ferreira 1978) and in Wales.

Occasional herbs include Agrostis stolonifera, Deschampsia cespitosa, Equisetum palustre, Chrysosplenium oppositifolium, Poa trivialis, Carex panicea, C. nigra, C. dioica and the rare Epilobium alsinifolium and Equisetum variegatum.