Contrary to the behaviour of the non-lichen forming Ascomycetes the lichen-fungi show very few cases of ordinary conidial formation.
In favour of the conidial view is the fact that in the case of Collema and a few other forms the spermatia have been made to germinate in artificial cultures, and in the case of Calicium parietinum Moller succeeded in producing a spermogonia bearing thallus from a spermatium.
Similarly with the various types of conidial or oidial "fructifications," termed pycnidia, spermogonia, aecidia, &c. In the simplest of these cases - e.g.
In other cases (Diplodia, Aecidium, &c.) conidial or oidial "fructifications" arise by a number of hyphae interweaving themselves into a knot, as if they were forming a sclerotium.
The development of the "conidia" as true conidial spores or as zoosporangia may occur in one and the same species (Cystopus candidus, Phytophthora infestans) as in Pythium described above; in other cases the direct conidial germination is characteristic of genera - e.g.