Define some features of Penicillium?
The identifying features of Penicillium are:
1. Mycelium consists of colourless, septate and branched hyphae, some of which grow inside the substratum to get nutrients and the rest spread on the surface. Former are called haustaria hyphae.
2. Erect, tubular septate hyphae called conidiophores grow outward in the air from any cell of the mycelium. No foot cells are present in Penicillium. Only one conidiophore arises from one cell.
3. Unlike Aspergillus, conidiophores branches once, twice or even more times to produce primary, secondary or tertiary branches. The ultimate branches bears tufts of flask shaped structures called sterigmata (phialides). These branches are called the metulae while lower branches which support the metulae are called rami. At the tip of the sterigmata, a long chain of conidia arise in a basigenous arrangement. The conidia are shed continuously. The conidiophore along with remi, metulae, sterigmata and conidia gives artist's brush or broom like appearance and the structure is called penicillus.
4. The conidia are tiny, uninucleate and unicellular, globose, solid, elliptical or pyciform structures. These may be smooth or rough.
5. Sexual reproduction is observed in a few species by formation of asci containing ascospores. Ascospores are uninucleate, lens shaped structures.