Scientific name Asplenium trichomanes – Ctenidium molluscum crevice community
Common name Maidenhair Spleenwort – Comb-moss crevice community
Community code RH1A


RH1A: Asplenium trichomanes – Ctenidium molluscum crevice community     RH1A: Asplenium trichomanes – Ctenidium molluscum crevice community     RH1A map: Asplenium trichomanes – Ctenidium molluscum crevice community

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This is a rather variable community with typically no dominants and with just three constant species, Sesleria caerulea and the calcicole mosses Tortella tortuosa and Neckera crispa. Ferns are a regular feature with Asplenium trichomanes frequently present while Asplenium ruta-muraria, Cystopteris fragilis and Phyllitis scolopendrium are all occasionally encountered. Asplenium viride is a rarer find. The main forbs are Geranium robertianum, Campanula rotundifolia and Thymus polytrichus, but the non-native species Epilobium brunnescens is also a feature here, particularly on wet cliff faces. Patches of Fissidens dubius and Breutelia chrysocoma are frequent additions to the bryophyte layer.



This is a sparsely vegetated rocky habitat community that occurs in range of habitats comprising crevices on calcareous cliffs, scree slopes and limestone pavements. Where pockets of soil have accumulated, they are skeletal and conditions are moist, base-rich and infertile.



There are two sub-communities described. Graminoids are generally more frequent in the Sesleria caerulea – Carex flacca sub-community (RH1Ai) than in the Tortella tortuosa – Asplenium trichomanes sub-community (RH1Aii) in which bryophytes tend to be more frequent. Sesleria caerulea is invariably present in RH1Ai but only occasional in RH1Aii.


Similar communities

Open limestone pavement vegetation is also represented by the RH1B Teucrium scorodonia – Mycelis muralis pavement community. However, Teucrium and Mycelis are much more frequent in that community, as are a number of woody species: Prunus spinosa, Hedera helix, Corylus avellana, Rubus fruticosus agg. and Rosa spinosissima. The present community also shares several species with the RH2D Angelica sylvestris – Breutelia chrysocoma ledge community, but that is an assemblage of wetter, less base-rich conditions where ferns are much less prevalent.


Conservation value

Many examples of this community qualify as EU HD Annex I habitat 8120 Calcareous rocky slopes but also included here are plots from the priority habitat 8240 Limestone pavement* and from habitat 8110 Eutric scree. In the uplands, this vegetation supports species with limited distributions in Ireland including Saxifraga aizoides and Orthothecium rufescens.



Accessible upland examples of this vegetation may be sheep-grazed. Climate change threatens arctic-alpine species which are restricted to upland sites. The impact of the non-native Epilobium brunnescens has not been investigated and hitherto no known management action has been taken. Limestone pavement sites are traditionally winter grazed by cattle and the main threats there are scrub encroachment, quarrying and destruction for purposes of agricultural improvement.