A herbarium record of Orthotrichum alpestre Hornsch. ex Bruch & Schimp. in Scotland: new to Britain

Knowledge of the genus Orthotrichum in Britain and Ireland has increased enormously in recent years, stimulated in part by the recovery of the epiphytic flora in regions formerly subject to high levels of SO2 pollution. This has led to the discovery of three species new to Britain, O. acuminatum, O. scanicum and O. rogeri (Blockeel, 2009, 2012; Bosanquet, 2015), the description of O. cambrense as a new species (Bosanquet & Lara, 2012) and the rediscovery of O. columbicum (previously known as O. consimile) after an interval of 160 years (Blockeel, 2008). With the exception of O. cambrense, which may be a stabilised genetic variant of O. tenellum, these newcomers have probably arrived as wind-borne spores from continental Europe, and have been able to grow to maturity because of improvements in air quality. In this paper we report a further species new to Britain, O. alpestre, but this latest addition differs in not being a recent arrival. It was collected in 1983 in north-east Scotland, a region that was little affected by air pollution during the twentieth century. The specimen was originally identified as O. pallens and was examined by T. L. Blockeel in 1998, who noted at the time that it was abnormal, being ‘atypical, strongly papillose.’ A detailed examination by F. Lara has now established its identity as O. alpestre. The nomenclature of bryophytes in this note follows Hill et al. (2008) and Lara & Garilleti (2014).