A new taxonomy of theCaloplaca citrinagroup in the Black Sea region is presented. It is based on the nrDNA ITS molecular data, chemistry (anthraquinone contents) and 20 morphological characters. Six species previously known in the region are accepted:Caloplaca arcis,C. calcitrapa,C. dichroa,C. flavocitrina,C. geleverjae,C. limonia. Five new species are described:Caloplaca arcisproxima,C. austrocitrina,C. communis,C. confusaandC. nigromarina. Seven further species,Caloplaca britannica,C. citrina,C. marina,C. maritima,C. microthallina,C. oraandC. phloginaare also treated briefly. Some maritime species known from the Atlantic coast of Europe are absent from the region, and, surprisingly,Caloplaca citrinas. str. could not be confirmed from the study area. A key to the species present in the region is provided, although morphological characters are of very limited value in this group. The variability and taxonomic importance of particular features are discussed. No significant differences in secondary chemistry were observed among the species.Many examples of convergence and some semi-cryptic species were revealed by molecular data. The term ‘semi-cryptic species’ is introduced here into lichenology for those species which cannot be clearly diagnosed by their morphology, but which are determined by other characters, mainly by their ecology and distribution. We propose to describe formally such species, in spite of difficulties with subsequent morphological identification.

T‐cell proliferation and function depends on signals from the antigen‐receptor complex (TCR/CD3) and by various co‐receptors such as CD28 and CTLA‐4. The balance of positive and negative signals de...