gogol

The fungi still present many unsolved phylogenetic problems. There is wide agreement that they are polyphyletic; that is, that there are as many plesiomorphs as there are independently originated groups of fungi. It also means that the evolutionary trends within this kingdom are complex. Polyphylesis of the fungi. In a phenetic approach, thefungi were classified into four divisions, i.e., Phycomycetes, Ascomycetes, Basidiomycetes, and Fungi Imperfecti. These divisions largely depended on reproductive structures, with the last being a catch-all for forms whose reproductive structures (and, therefore, life cycles) were unknown. This approach did not satisfy those who felt that classification should be more than just a way to store and retrieve information, i.e., that it should also reflect evolutionary history.

We see here that the Phycomycetes are missing, and in their place are three other divisions. These are thought to be close to monophyletic groupings. The Fungi Imperfecti, now designated Deutoromycota, are accepted as probably having no sexual reproduction; they reproduce asexually by spore-formation and elongation of hyphae. Then three unusual groups are placed here, but there is no real conviction that they are genuine fungi. The first of these are the lichens. There are 15,000 to 20,000 species of these organisms, which represent symbiotic relation between a fungus and an alga and show identifying features from the blue-green and green algae and from the Basidiomycota, Ascomycota, and Deuteromycota. Obviously, classification and evolutionary relations are difficult beyond the recognition that their status is special and that they are arbitrarily put in with the fungi. The other two groups are the cellular slime molds and the plasmodial slime molds, which seem to have independent origins. Both have a sporeforming stage that is fungal in appearance, which is now believed to represent convergent evolution. Both have an ameboid stage in their fife cycle, during which feeding is by phagocytosis. In this stage their character is clearly that ofunicellular ingestor or animal, which strongly indicates a protozoan nature. In fact, many schemes of protozoan classification include the slime molds. They are included here only because they are commonly classified among the fungi; it is an Adansonian solution to their taxonomic status, not an evolutionary one.

There remains the two major divisions of the Ascomycota and Basidiomycota. These, plus the former Phycomycophyta, are often combined into one division as the Eumycophyta or true fungi. It is within this grouping that phylogenetic trends, if they can be studied anywhere in the fungi, are most apparent.