Commoness-rarity has been expressed on a 9-class scale, as follows:
a: absent
er: extremely rare
vr: very rare
r: rare
rr: rather rare
rc: rather common
c: common
vc: very common
ec: extremely common
Commoness-rarity was calculated, for each of the 9 phytoclimatic OGUs, on the basis of three main criteria: a) number of samples in the TSB lichen herbarium (% on the total for a phytoclimatic area), b) number of citations in the literature, c) an expert judgement used in particular cases (e.g. that of recently-described taxa for which few literature records are available). A detailed explanation of the methodology will be presented in a forthcoming paper. The "er" class was adopted for lichens which are known from less than five stations, and/or were not found in recent times, excluding most recently-described species, and taxonomically very poorly known taxa. The total number of states for this parameter is 81 (9 commoness-rarity classes x 9 OGUs).