Both Penicillium and Acremonium ( = Cephalosporium) are common and widespread in soil; they are particularly associated with senescent and dead plant material, so that the majority of floristic studies of a wide range of soil types and plant surfaces include species of these genera in the lists of fungi isolated. Although the two genera are especially associated through the production of β-lactam antibiotics by one, or at the most a few, species, they differ markedly in the visual impact that they make when growing as colonies on plates of solid media. On the one hand, mature colonies of Penicillium are characterized by the production of large numbers of dry conidiospores that are usually gray-green to blue-green, although strains of P. camembertii may remain persistently white and P. humuli has a distinctly brownish coloration. Colonies of Acremonium, on the other hand, are characterized by their pale colors—often turning pink or orange, although A. butyri produces pale yellow-green colonies—and the production of wet or slimy spores.