The kingdom Fungi contains four major divisions that were established according to their mode of sexual reproduction. Polyphyletic, unrelated fungi that reproduce without a sexual cycle, are placed for convenience in a fifth division, and a sixth major fungal group that does not fit well with any of the previous five has recently been described. Not all mycologists agree with this scheme. Rapid advances in molecular biology and the sequencing of 18S rRNA (a component of ribosomes) continue to reveal new and different relationships between the various categories of fungi.
The traditional divisions of Fungi are the Chytridiomycota (chytrids), the Zygomycota(conjugated fungi), the Ascomycota (sac fungi), the Basidiomycota (club fungi), and the Deuteromycota (imperfect fungi). The Glomeromycota belong to a newly described group (Figure 13.24).