Pithomyces conidia

Pithomyces is a genus of asexual ascomycetes. Recently, molecular analysis has resulted in the genus being split into two genera, Pithomyces and Pseudopithomyces. The conidia produced by these fungi generally occur in low numbers in Tulsa outdoor air samples and are seldom found as an indoor contaminant. These fungi are mainly saprobes on decaying plant material although some species have been reported causing leaf spot disease. The spores are thought to be allergenic but have not been well studied. 

Pithomyces/Psuedopithomyces conidia are multicellular and dark brown. The most commonly seen conidia have both transverse and longitudinal septa, although a couple of species are reported to only have transverse septa. Also during development, the transverse septa develop before the longitudinal ones. (See the bottom photo below.) Therefore, if immature conidia become airborne, only transverse septa may be visible. Conidia are produced individually, and a short attachment stub is often visible at the base where the conidium detached from the conidiophore. In two of the three images below, this attachment stub can be seen above the arrows.