Fungi Classification

How should the fungi (fungus) be characterized? While it is a concern in classification to put together those organisms that are related to one another by descent from a common ancestor, this is certainly not the case with fungi. While these organisms do share certain traits, this does not imply kinship.

All fungi lack chlorophyll. They can be unicellular, multicellular, or acellular. The cell walls often have chitin similar to the chitin found in insects and crustacea. Cellulose may also be present.

In the five kingdom system, the fungi are awarded the status of kingdom. It is not a perfect arrangement and it does not suggest that the things called fungi are related to each other by common origin; rather, it is a way to keep track of these organisms. Some researchers subdivide Fungi into five classes, some six, and some seven: Chytridiomycetes, Oomycetes, Zygomycetes, Ascomycetes, Basidiomycetes, and for want of a better place to classify them, the Fungi Imperfecti and perhaps the Lichens (which, though certainly not fungi, do keep the company of fungi). Sometimes, the first three of these- Chytridiomycetes, Oomycetes, and Zygomycetes-are considered one class: the Phycomycetes. This scheme, which designates these three as subclasses, is the one adopted in this text.

Fungi are classified according to the kind of fruiting body produced in the sexual phase of reproduction. Phycomycetes produce zygospores: Ascomycetes produce asci, and Basidiomycetes produce basidia. Both asexual and sexual methods of reproduction take place, although different terminology is used describe these functions in fungi. The asexual method is called the imperfect stage, and the sexual method is called the perfect stage. Zygospores, asci, and basidia are produced during the perfect stages of the reproductive cycle.

For purposes of illustration in this discussion, two groups of fungi will be considered: Myxomycetes (the slime molds) and Eumycetes (the true fungi). (This ignores the cellular slime molds, which include Acrasinomycetes and Labyrinthulomycetes.)