in Basidiomycetes (e.g., Agaricus), karyogamy and meiosis take place in the basidium producing four basidiospores. The text explicitly states, 'The basidiospores are exogenously produced on the basidium.' In contrast, in Ascomycetes (e.g., Neurospora, Saccharomyces), sexual spores called ascospores are produced endogenously in sac-like asci. Alternaria belongs to Deuteromycetes, where only asexual or vegetative phases are known.