Penicillium

Species of Penicillium are recognized by their dense brush-like spore-bearing structures. The conidiophores are simple or branched and are terminated by clusters of flask-shaped phialides. The spores (conidia) are produced in dry chains from the tips of the phialides, with the youngest spore at the base of the chain, and are nearly always green.

Branching is an important feature for identifying Penicillium species. Some are unbranched and simply bear a cluster of phialides at the top of the stipe. Others may have a cluster of branches, each bearing a cluster of phialides. A third type has branches bearing a second order of branches, bearing in turn a cluster of phialides.

These three types of spore bearing systems (penicilli) are called monoverticillate, biverticillate and terverticillate respectively. Penicillium is a large and difficult genus encountered almost everywhere, and usually the most abundant genus of fungi in soils.