One of two dioicous species of Pellia – the other is P. endiviifolia – and there is no problem identifying it with confidence when female thalli with more or less untoothed involucral flaps are present, usually in spring.
Male plants are a little more challenging. If antheridial pits extend nearly to the apex of the thallus and there is no involucral flap then it is unlikely to be P. epiphylla, our only monoicous species . But how to separate from male P. endiviifolia if the thalli are unbranched? There are two good ways. Firstly, the antheridial pits of P. neesiana always look very conspicuous because there are raised, papilliform cells surrounding the pit aperture (see Claire’s excellent close-up images of this feature below). P. endiviifolia does not have these conspicuous cells and so its antheridial pits are less obvious.
P. neesiana also has very short slime hairs – typically only one cell below the terminal slime papilla. This is a character shared with P. epiphylla. Slice off the end of a healthy-looking and relatively clean thallus and squash it lower side uppermost under a cover slip on a slide and you should see some under high power. P. endiviifolia has longer slime hairs formed of 2-4 or more cylindrical cells below a terminal slime papilla. More information about these useful slime hairs is given in Frahm’s 2013 paper, which can be downloaded from this page.
The oft-quoted aroma of fresh P. neesiana cannot be detected by everyone.Read the Field Guide account