In Collema and a form like Xanthoria parietina it is probable that actual fertilization takes place, and possibly also in some of the other forms. It is probable, however, that in the majority of cases the ascogonia develop without normal fertilization, as is necessarily the case where the ascogonia have no trichogynes or the spermatia are absent.
- Vertical Section of Apothecium of Xanthoria parietina.
Xanthoria parietina has been known to grow for fortyfive years before bearing apothecia.
The so-called chrysophanic acid found in Xanthoria (Physcia) parietina is not an acid but a quinone and is better termed physcion.