Identification notes
When Eric Watson revised his 3rd (and final) edition of British Mosses and Liverworts in 1981, this species (as M. temperata) had only recently been recognised as distinct from M. violacea (then M. fruticulosa) and so was given a single sentence in a footnote to M. furcata. In the decades since, M. consanguinea has been recognised as a relatively common species, and, with M. violacea, one of two epiphytic species of Metzgeria that have narrowed, gemmiferous shoot apices.
There is usually no problem identifying strongly gemmiferous M. consanguinea. However, rain can wash off gemmae and until they have grown back, it may be surprisingly difficult to tell this plant apart from M. violacea in the field. The tip of the attenuated thallus is normally slightly broader than that species, which may help, but otherwise examination of collected plants under a stereomicroscope later will usually confirm the position of any gemmae.
You can also examine the nerve of an attenuated branch under a microscope and count the number of (longitudinal) rows of epidermal cells overlying it. M. consanguinea has 2 rows, compared to 3-6 in M. violacea.
Read the Field Guide account