Colonies with more or less well developed, colourless, simple or branched conidiophores bearing two to several phialides. The phialides are characteristically swollen at the base and gradually narrowed into a long beak. The spores (conidia) are produced in chains from the tips of the phialides, are colourless or brightly pigmented, and are usually rather narrow. Similar to Penicillium, but the chains of spores tend to be widely divergent in Paecilomyces and more parallel in Penicillium. Species of Mariannaea are similar to those of Paecilomyces, differing in producing whorls of metulae and phialides along a vertical axis.