The use of ascoma ontogeny in the systematics of lichenized ascomycetes is reviewed briefly. Two recently studied examples are discussed to illustrate the use of ontogenetic studies to discover phylogenetic relationships. As one example, the Agyriaceae was mainly circumscribed by the ascus type and included diverse genera. Xylographa is characterized by lirelliform apothecia. However, the ascoma development shares the ontogenetic pattern observed in Trapelia and its placement in the family was confirmed. In contrast, Anamylopsora exhibited a substantially different apothecial development and was separated as a family of its own. As a second example, the Candelariaceae is based on chemical characters. With the detection of pulvinic acid derivatives also in the genus Lecanora, the distinction of the Candelariaceae and Lecanoraceae became doubtful. Therefore, the ascoma ontogeny was employed to evaluate this classification and is illustrated here in detail for Candelaria fibrosa. The substantial similarity of the ascoma development found in both families suggests that both might be better united. Finally, a general discussion of the significance of ontogenetic characters in lichen taxonomy is included.