Bryum creberrimum

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Identification notes

Bryum is a large and confusing genus and it’s understandable that many bryologists avoid collecting Bryum specimens out in the field.

However, if you come across a relatively robust Bryum with mature capsules growing on soil, it’s often worth trying to identify it as the chances are it could be an  uncommon species. Most of the capsule-bearing plants you’ll find are likely to be Bryum dichotumum, a much smaller species. Bryum capillare, another ubiquitous lowland moss, prefers to grow on hard basic substrates rather than soil.

Bryum creberrimum is a species that deserves more attention – if only for the intricate beauty of its peristome structures (see the images below). Although it’s considered to be rare, it is very likely overlooked and could certainly be more common, especially in the south-east of England.

Shoots look most similar in the field to B. pallescens but they can only be identified accurately by examining peristome and spore characters. Both species have synoicous inflorescences – the Bryum pallescens page has an explanation of this, with images, and also describes how to examine peristome structures microscopically. B. creberrimum differs critically from B. pallescens in the shape of the holes, or perforations in the upper part of its delicate processes (endostome segments/teeth). These are about as wide as long, whereas they are normally longer than wide in B. pallescens.

Distribution in Great Britain and Ireland

This moss often grows in unremarkable, dry open habitats where bryologists don’t often go. Think lowland gravelly banks, waste ground, wall crevices and even flower-pots. A substantial and thriving population of B. creberrimum was found in 2022 on a living roof of a tower block in the former 2012 Olympics Athlete’s Village in London.

View distribution from the BBS Atlas 2014

Resources you may find useful

Holyoak, D. 2021. European Bryaceae.

David Holyoak’s book contains keys, detailed morphological, ecological and taxonomic descriptions and diagrams showing key features – and is highly recommended for anyone wishing to get to know Bryum species.

The Bryophyte identification page under Resources contains additional information on the genus Bryum, including an early version of the keys now published in David Holyoak’s book.

Bryophyte identification resources

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