Identification notes
For many years this species hid in plain sight as a form of P. porelloides and was not recognised as a distinct taxon until 1979 – Jean Paton’s paper is cited below. An important difference from P. porelloides (and P. asplenioides) is the much large leaf cells of P. britannica, and with practice, candidate plants may be recognised from this character in the field.
Among other differences, one of the best is the way the leaves are inserted on the stem. Check the upper surface of a well-grown shoot with a hand-lens. Do the decurrent leaf bases run down the stem in a slightly curved line (P. porelloides, P. asplenioides) or a straight one (P. britannica)? Plants of P. britannica also look different enough from both species to pique curiosity and in some forms at least, they grow in a way that is reminiscent of the unrelated Saccogyna viticulosa.
