Ontogenetic development of pycnidial conidiomata and conidium formation in the genus Peltigera ( Ascomycota , Peltigerales )

We studied the rarely occurring pycnidial conidiomata in three species of the genus Peltigera using electron microscopy (SEM and TEM). Pycnidia are marginal and half-immersed, having unilocular cavities with double-layered walls and slit-shaped ostioles. The conidiophores are composed of sterile basal and very few axial cells, supporting elongated conidiogenous cells. The conidia are produced at their apices by leaving behind phialidic collarettes either at the same level or in a proliferating manner, extending the conidiogenous cells. The study of the ontogeny of the pycnidial conidiomata demonstrates the origin and the gradual development of the characteristic anatomical structures, such as the wall layers, the bursting ostiole, and the non-chambered cavity, which is completely lined by the conidia-forming elements. The combination of these morpho-anatomical details is unique and hence accepted here as ‘ Peltigera -type’, in addition to previously recognized pycnidia types (Vobis 1980).