Weissia wilsonii

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Identification notes

Weissia wilsonii replaces W. multicapsularis, which in 2019 turned out to be erroneously based on a mixed collection of W. longifolia and Tortula acaulon.

W. wilsonii is a pioneering species that grows as scattered stems or in loose cushions similar to W. longifolia. Both species have long, relatively broad perichaetial leaves which often partially obscure the cleistocarpous capsules. The most important diagnostic character of W. wilsonii is the large operculum (lid), although there is a small amount of overlap with W. longifolia. Care must be taken to measure the length of the operculum rather than the calyptra, if present, as it is much larger. Shoots can have more than one capsule and then W. wilsonii may resemble W. sterilis, often a larger plant with longer stem leaves.

Distribution in Great Britain and Ireland

Although not a common species, a number of new populations of W. wilsonii have been found recently and it is undoubtedly more widespread than W. multicapsularis (a Nationally Rare species) was. Examination of herbarium specimens of  W. longifolia var. longifolia in 2021 confirmed that nearly 20% belonged to W. wilsonii instead. An analysis of how under-recorded W. wilsonii is likely to be was published in Field Bryology in 2022 and can be downloaded from the link below.

View distribution from the BBS Atlas 2014

Resources you may find useful

Callaghan, D.A., Bell, N.E. and Forrest, L.L. 2019. Taxonomic notes on Weissia subgenus Astomum, including Weissia wilsonii D.A.Callaghan, a new species from Europe. Journal of Bryology 41: 135-148
Callaghan, D.A. 2022. How under-recorded is Weissia wilsonii in Britain? Field Bryology 127: 24-25

Des Callaghan updates what is known about the distribution of W. wilsonii in early 2022, based on redeterminations of historical herbarium specimens of W. longifolia.

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