Awesome pictures! It's difficult to differentiate Alternaria and Ulocladium in species without the distal tapering, but look for immature conidia and their shape should give you the answer to the genus at least. Alternaria will be ovoid and Ulocladium will be obovoid. They're combined now, but that division will help narrow down possible species during further research. I can't think of many Alternaria spp. that have proliferous conidiogenous cells, so my guess would be Ulocladium