Constant species

Arrhenatherum elatius, Festuca rubralovina, Geranium robertianum, Gymnocarpium robertianum, Teucrium scorodonia, Ctenidium molluscum.

Physiognomy

The Gymnocarpietum robertiani comprises more or less open stands of fern- and grass-dominated vegetation disposed over the distinctive topography of limestone screes and pavement. Scattered fronds of Gymnocarpium, arising separately from the creeping rhizomes, begin to emerge rapidly in late spring, their rather stately forms attaining up to 40 cm or so in height. Among these, occasionally in some abundance, are loose tussocks of Arrhenatherum and, less commonly, Festuca ovinalrubra (not distinguished in available data) and Brachypodium sylvaticum. In sunnier situations, which the fern seems to tolerate well, perhaps because of its somewhat mealy surface (Page 1982), the Brachypodium often has a rather lurid yellow-green tinge. Sesleria albicans does not appear in the table because samples of the community were not collected within the range of this grass but it can figure prominently in this vegetation in the Yorkshire Dales and southern part of the Lake District.

Other very frequent components are Geranium robertianum, commonly showing a reddish hue to its stems with the typically impoverished nature of the substrate, Teucrium scorodonia, Mycelis muralis and Mercurialis perennis. Where clonal patches of the last plant thicken up, the Gymnocarpium seems to suffer and be gradually eclipsed (Page 1982). Less common vascular associates include Origanum vulgare, Carex flacca, Viola riviniana, Senecio jacobaea, Oxalis acetosella, Arabis hirsuta and, in the northern Pennines, Galium sterneri.