Identification notes
An alternative common name for this species could be ‘black graffiti-wort’ for it often does look like dark scribblings on rock. When you find it, on sheltered, shady dry limestone or other base-rich rock, it often forms dense, really dark patches and is usually instantly recognisable.
However, Porella platyphylla can be an imposter, sometimes creeping across rock and looking just like M. mackaii. So it’s always worth just prising a shoot off the substrate and turning it over to make sure the underleaves and lobules belong to the right species.
Read the Field Guide account