Plectomycetes

(mycology) A class of the subdivision Ascomycotina, members produce a well-developed mycelium on which both sexual (asci) and asexual (conidia) states occur.

A class of the phylum Ascomycota. The Plectomycetes produce a well-developed mycelium on which both sexual (asci) and asexual (conidia) states occur. The asci form in association with small ascomata of varying complexity. These arise from special coiled or intertwined hyphal branches that are sometimes differentiated into male (antheridium) and female (ascogonium) structures. The ascomata may consist of a loose grouping of hyphae around the asci forming a gymnothecium, or may be spherical, with a definite wall or peridium that lacks an opening, forming a cleistothecium. The asci are usually spherical, are scattered throughout the ascoma, and have thin walls that dissolve at maturity. The ascospores are small, colorless or sometimes pigmented, round in face view, somewhat flattened in side view, and may be ornamented or flanged.

The two recognized orders, Onygenales and Eurotiales, are differentiated by the structure of the ascoma and the type of asexual conidia produced. In the Onygenales, the ascoma usually is not well developed (gymnothecium), but many species form characteristic peridial hyphae. These fungi occur in soil, on dung, and on plant debris. The most serious fungal pathogens of humans belong in the Onygenales. Arthroderma simii. In the Eurotiales, the ascomata have a definite wall (peridium) enclosing the asci, and they are often brightly colored. They are common in soil and on plant materials. The most important species is Penicillium chrysogenum, the original source of penicillin. See also Ascomycota; Eumycota; Fungi.