Identification notes
Well-grown plants growing in flushes and marshes with associates such as Bryum pseudotriquetrum are normally easily recognised as P. fontana. However, this species is morphologically variable and almost certainly every bryologist has been fooled by it at some point.
Small, poorly grown forms are easy to misidentify as one of the smaller species – P. caespitosa especially – and this often comes down to the leaves of such plants lacking fully developed marginal teeth and cell mamillae.
Large forms of P. fontana can grow in strongly calcareous places, for example with Palustriella species in base-rich flushes and can have quite secund leaves, so are easy to mistake for the uncommon P. calcarea. Leaf characters including nerve width and cell size will however confirm any provisional identification.
When examining any Philonotis, it is always the mature leaves from the previous season among the stem tomentum that should be selected. Younger leaves higher up on the stem (or anywhere on small, possibly juvenile plants) should be ignored. You’ll also need to have a compound microscope with good quality optics and illumination to clearly see cell mamillae – basic microscopes usually aren’t good enough.
Beware confusion with Pohlia wahlenbergii on damp tracks. The best way to tell them apart is to see if marginal leaf teeth are single (Pohlia) or double (Philonotis) and is the nerve is weak (Pohlia) or strong (Philonotis).
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