The image here represents a Pilobolus zygosporangium from the phyla Zygomycota (See links page). Once again, biologists have largely overlooked the phyla Zygomycota. The group consists of two classes, the Zygomycetes and Trichomycetes. The Trichomycetes is an unusual group of fungi that are ecologically and morphologically distinct from all other fungi. They attach to the gut wall of aquatic arthropods or the aquatic larval stages of terrestrial insects, most probably feeding on the stomach contents - the exact nature of the relationship between the fungi and 'host' being unknown. The group is divided into four orders; the Harpellales, Amoebidiales, Asellariales and Eccrinales. 

The Zygomycetes are divided into seven orders; the Mucorales, Entomophthorales, Dimargaritales, Kickxellales, Endogonales, Zoopagales and Glomales. In general, the Zygomycota are typically mycelial and non-septate (though septa are present in some subgroups), some species are both hyphal and yeast forms. Sexual reproduction is by the fusion of sex organs (gametangia) leading to thick walled resting spores known as zygospores, which germinates after meiosis to form a hypha. It is this character which is unique to Zygomycota. Asexual reproduction is by cytoplasmic cleavage in a sporangium, forming non-motile spores.

The subgroup Mucorales certainly has the largest number of species and morphological diversity of the other seven orders, and is the best known. Most members of Mucorales are saprobes that occur in dung, soil and humus. However, the most significant group in the Zygomycota, evolutionary speaking, has to be the Glomales. Members of Glomales establish myycorrhizal relationships with most angiosperms, some gymnosperms, bryophytes, pteriodophytes and even some algae. In return for a source of carbohydrates from the plant, the fungi provide their associate with increased uptake of water, nutrients and metabolites via their extended hyphae. Data from 18S ribosomal DNA sequences indicates early divergence of the Glomales (Zygomycota) from the Ascomycete/Basidiomycete clade, approximately 500-600 million years ago. The subsequent divergence of Ascomycota from Basidiomycota came after the origin of the Glomales. This therefore indicates, since radiation of the above three fungi probably occurred after the origin of land plants, Glomales was the first divergence of terrestrial fungi.