Description of fungi
 

• The conidiophores of Penicillium are hyaline, smooth and swollen at the top. They have one or more whorls on which 10 to 16 phyalids are attached (Figures 1 and 2). These bottle-shaped phyalids can be produced alone by the conidiophore or from metules (Figure 3).
• The conidia are formed from the phyalides on top of which they are assembled into compact long columns. Each unicellular conidium measures 3-3.5 µm in diameter. They are smooth and globular, most often dull green. Very easily transportable by the wind, the conidia are released in the form of a cloud of green dust.
• The penicillus , a characteristic structure of Penicillium spp., Is made up of all conidiophores, metules, phyalids and conidia.
• Several types of ramifications are possible in Penicillium spp .. Some are monoverticillate, or unbranched, others are biverticillate, which corresponds to the appearance of a branching level, or even triverticillate (2 branching levels) . This character contributes to the discrimination between species. It is also at the origin of the "brush" or "brush" appearance of the fruiting of Penicillium bodies observed with a binocular magnifying glass or with a microspcope. For example, P. expansum is triverticillate (figure 3) while P. frequentans is monoverticillate.
• Appearance of the colonies on malt-agar medium : they grow rapidly on malt-agar medium and exhibit a powdery appearance corresponding to the dense felting of conidiophores. In general, cultures Penicillium are stained in shades of green (Figure 4). P. expansum forms a dark green colony with an orange to light brown underside. A very characteristic rotten apple smell emanates from it.