Cetrelia olivetorum (Nyl.) W.L. Culb. & C.F. Culb.

(Figs 2; 5D; 10-12)

It is the easiest of the four species to identify because olivetoric acid produces a characteristic, water repellent spot on the chromatographic plate, although a wider species concept previously (Wirth 1980; Verseghy 1988, 1994, Smith et al. 2009) also was applied for specimens not containing olivetoric acid (here revised mostly as C. monachorum by HPTLC). Cortical atranorin is also present. This species forms soredia varying from fine to coarse, 36.4 ± 9.5 µm in Hungarian samples [versus 25-55 µm diam. inObermayer & Mayrhofer (2007)], while pseudocyphellae – if any – are rare on both upper and lower cortex and small (20-50 µm).

This species was collected from rocks (39%), but was mostly found on bark of Quercus (13%), Fagus (9%) and various unidentified trees (39%) at 100-800 m a.s.l. It is the second most frequent species of Cetrelia, known from a moderate 26 collections (Figs 10; 11). Cetrelia olivetorum is proposed as vulnerable (VU) in the Hungarian red-list.