Since Alternaria species are cosmopolitan and ubiquitous in nature, they are also common laboratory contaminants. Macroscopic Features Alternaria spp. The colony is flat, downy to wooly and is covered by grayish, short, aerial hyphae in time. The surface is greyish white at the beginning which later darkens and becomes greenish black or olive brown with a light border. Microscopic Features Alternaria spp.
Conidiophores are also septate and brown in color, occasionally producing a zigzag appearence.
These conidia may be observed singly or in acropetal chains and may produce germ tubes. They are ovoid to obclavate, darkly pigmented, muriform, smooth or roughened. The end of the conidium nearest the conidiophore is round while it tapers towards the apex. Alternaria alternata Alternaria geophilia Alternaria spp. Compare to Ulocladium , Stemphylium , Pithomyces , Dissitimurus , synanamorphic forms of Phoma .