File:Maidenhair spleenwort (Asplenium trichomanes) - geograph.org.uk - 989075.jpg

English: Maidenhair spleenwort (Asplenium trichomanes) [For a more precise identification, see the end of this item.]

Several of these ferns were growing on the side of a small rocky overhang. These plants are surprisingly small: for example, the whole tuft of fronds shown here measures just ten centimetres across, and the individual fronds are less than a centimetre wide. Others ferns of the same species located nearby were of a similar size, or even smaller.

The brownish stalk (or "rachis") distinguishes this fern from the otherwise similar Green spleenwort (Asplenium viride), which has a green rachis.

There are three British subspecies of A. trichomanes, namely, quadrivalens, trichomanes, and pachyrachis [see, for example, "The Fern Guide" by J. Merryweather, 3rd edn., 2007, Field Studies Council, in the AIDGAP series].

Based on the nature of the rock on which this is growing (one of a series of cornstone outcrops to be found in this area along an E-W line - https://www.geograph.org.uk/photo/1253323 ), this is evidently Asplenium trichomanes subsp. quadrivalens, which grows on lime-rich rocks (and on mortar in walls). The pinnae (the smallest leaflets) are oblong, and are borne at an angle to the plane of the frond. They remain on the rachis (the stalk) until the stalk itself is shed in winter.

[Subsp. trichomanes, in contrast, grows in a lime-free habitat, and has more rounded pinnae which are in the plane of the frond; these pinnae are shed, to leave bare stalks. The remaining subspecies, pachyrachis, does not occur in this part of the UK.]