A globally rare species on old deciduous trees. The deterioration of its habitat is caused by human activities. Proposed and data compiled by Göran Thor.

Suggested assessment by proposer: VU on the A criterium (A2bc+3bc+4bc), population decrease 30 (20-50) % over 100 years. When searched for in southernmost Sweden in the 1990’ it was only refound on 20% of the old localities. The situation is the same in most of Europe, especially in the lowland.

Bacidia rosella is widely distributed on deciduous trees in most of Europe except the westernmost part and it also occurs in North Africa. The reports from North America refer to the newly described Bacidia rosellizans.

The species has decreased rapidly in most of its distribution area and is red-listed in e.g. Austria, Denmark, Germany, Italy, Norway, Sweden and Switzerland.

The species is found on old trees of Fagus sylvatica, Acer platanoides, Ulmus spp. and Quercus spp., rarely also on other tree species. The species occurs both in open and closed forests as well as in avenues and church yards. The species is only found on humid localities with long tree continuity.

Localities with long tree continuity and deciduous trees are decreasing all over Europe. It is most probably also sensitive to air pollution. The Dutch elm disease is a threat for the occurrences on Ulmus spp.

Rich localities should be protected and managed in a way that supports the species.

ArtDatabanken. http://www.artfakta.se/Artfaktablad/Bacidia_Rosella_134.pdf

The Information System on Italian Lichens. http://dbiodbs.univ.trieste.it/italic/italic03

Rote Listen Deutschland.  http://www.bfn.de/0322_rote_liste.html

Red Lists: Threatened species in Switzerland. http://www.bafu.admin.ch/publikationen/publikation/01688/index.html?lang=en