Identification notes
This species often appears smaller than P. spinulosa and larger than P. punctata, and its defining field characters can be quite hard to describe. It will grow in drier places than both of those species and a P. spinulosa-like form on hard limestone or rocks in coastal districts will often be P. bifaria. Shoots often look quite compressed too but by far the most reliable identification character is the presence of a line of elongated cells (the vitta) in the middle of the leaf base. This can be seen at relatively low magnification once leaves have been stripped off, so is not difficult to check.
Read the Field Guide account