This is a really common thalloid liverwort but like its two sisters – P. epiphylla and P. neesiana – it can only be confidently identified in the field when reproductive structures are present, or when its winter branching is endive-like (hence the specific epithet of P. endiviifolia). Without these branched plants, you’ll need to determine two things – whether the plants are monoicous or dioicous (of the three species P. endiviifolia and P. neesiana are dioicous, so have separate male and female plants) – and, if dioicous, what the edge of the perianth flap looks like.
Quite often, sterile and little-branched Pellia plants are encountered and under these circumstances there is another, little-known means of separating P. endiviifolia from the other two species. This is by cutting off the tip of a thallus and squishing it under a cover slip on a slide. If it is P. endiviifolia, you should see small slime hairs formed of 2-4 or more cylindrical cells below a terminal slime papilla at the edge of the thallus. If very short slime hairs (one cell below a slime papilla) are present then it has to be either P. epiphylla or P. neesiana. More information about these slime hairs is given in Frahm’s 2013 paper, which can be downloaded from this page.Read the Field Guide account