Towards a better knowledge and conservation of cryptic macrolichens in Italy: a revision of the genus Cetrelia (Parmeliaceae, Lecanorales, lichenized Ascomycota)

Cryptic species are a challenge for conservation since their ambiguous recognition can hinder a reliable evaluation of their distribution and ecology, thus affecting the assessment of their conservation status. <i>Cetrelia</i> W.L. Culb. & C.F. Culb. is a foliose chlorolichen genus with four species in Europe, which represents a good case-study on this issue. All four sorediate <i>Cetrelia</i> species are morphologically very similar and also show a similar ecology. They can be identified by chemical characters related to their distinctive secondary metabolites, whose diagnostic value is also supported by molecular data. In addition, they are overall rare, and therefore virtually endangered, although in previous assessments they were evaluated as "data deficient" due to the scarcity of available data. The few, old literature records in Italy refer almost exclusively to one species (<i>C.olivetorum</i>), which, however, has been shown to be quite rare in other European countries. To better elucidate the actual distribution of the four species in Italy, we carried out a revision of all the available herbarium specimens and checked several new collections from the main centres of distribution. We analysed 320 specimens from 59 sites, confirming the occurrence of all the four species reported from Europe. <i>Cetreliamonachorum</i> is the most widespread, ranging from the Alps to the Apennines and Sardegna. <i>Cetreliacetrarioides</i> is less widespread, occurring across the Italian Alps. <i>Cetreliaolivetorum</i> is confined to the Eastern Alps and northern Apennines. <i>Cetreliachicitae</i> is the rarest, being found only in five sites in the Central and Eastern Alps. All the four species dwell in old, moist montane forests dominated by beech and/or conifers and with long ecological continuity, but they show different biogeographical patterns, which should be considered for planning conservation actions. All the sites hosting <i>Cetrelia</i> species, especially those in which more than one species occur, would deserve protection.