Identification notes
Bryologists have wrestled with what has become known as the Bryum dichotomum complex of bulbiliferous species for many years. Species have been described within that are no longer accepted (eg B.dunense), others are recognised on continental Europe but not in Britain and Ireland (eg B.barnesii), and new species have been described which are now accepted (eg B.dyffrynense). Bryum gemmiferum and Bryum gemmilucens are distinctly different and are generally accepted as good species. Within what we now call Bryum dichotomum there is a great variation in leaf characters but all have greenish bulbils in groups of up to 20 per axil (usually far fewer), with clear leaf primordia.
Bryum dichotomum is a very common species of disturbed ground that is tolerant of eutrophication and sometimes thrives on it. It is frequent beside paths, tracks, roads and in arable fields. When bulbils are present identification is usually straightforward, but it is not uncommon to come across plants with no bulbils which can be perplexing due to variability of this species. Some may be impossible to name with certainty.
There is a most curious form with clusters of stipitate (stalked) structures in the lower leaf axils, which change colour as they mature. Originally found in Cornwall, then in the Netherlands, it has now also been found on the Isle of Wight. It was originally thought but these were gemmae, but work by George Greiff w
has demonstrated that these are in fact chytrid (fungal) galls, generated by a species of Synchytrium.
Molecular taxonomy is likely to shed more light on this species complex with the strong possibility of cryptic species being present.
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