Growth and development of ascomata in two species of Arthoniales, Arthonia calcarea and Alyxoria varia (Lichenized Ascomycota: Arthoniaceae and Lecanographaceae)

The growth of ascomata in two opegraphoid lichens, Arthonia (Opegrapha) calcarea and Alyxoria (Opegrapha) varia was determined using sequential photography over a period of 36 years. Arthonia calcarea produced ascomata over the entire period and began to appear less than 18 months after thallus establishment. The growth rate of Alyxoria varia ascomata declined with age and mature ascospores appeared about 10 months after ascoma initiation. Ascomata reached maturity at c. 5 yr after which ascus density within the pseudohymenium declined, although individual ascomata may persist for a decade or more. Ascus density was greatest in the smallest ascomata sampled (<0.5 mm long).