A rare Glamorgan fern at Tonyrefail

December isn't exactly the busiest month on the field botanist's calendar, but just occasionally it turns up something as interesting as any summer month!

A couple of weeks ago, a circular walk from Tonyrefail in the late afternoon gloom took me past a bank on which was growing an odd-looking fern, with the overall appearance of a small Lady Fern (Athyrium filix-femina) but with the more leathery leaves and linear sori (groups of spore-cases) characteristic of the spleenworts (Asplenium spp.). A return visit and closer inspection confirmed my initial suspicions, that this was the county rarity Lanceolate Spleenwort (Asplenium obovatum).


Fresh fronds of Asplenium obovatum at Tonyrefail - this was one of the larger plants.

This somewhat obscure species is most closely related to Black Spleenwort (Asplenium adiantum-nigrum), from which it differs in the smaller, paler-green fronds that taper at both ends, the shorter petiole, and the blunter pinnules.



Pressed specimens of Asplenium obovatum. The tendency of the lowest pinnules to be smaller - and to deflex slightly - is evident in the top frond (which has its top surface uppermost), while the bottom frond shows the clusters of spore-cases that mark it out as being an Asplenium.

The plants were growing on a lightly-vegetated south-facing retaining bank, with plenty of exposed stone. I'm familiar with this species from West Devon, where it is local in exactly the same habitat. The Tonyrefail population seems to be quite healthy, with over 40 plants of various sizes.


The retaining stone wall on which Asplenium obovatum was growing - the pale-green fronds caught my eye.

Asplenium obovatum has only ever been known from four sites in Glamorgan. Of these, only two seem to be extant - one at Penmaen in the Gower and another localised only to ST19M (jointly Glamorgan & Monmouthshire)... so it was a nice botanical 'Christmas present' to add another site to this list!