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.