The Wonderful World of Fungi

Part VII – Division Ascomycota – Introduction

By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
AAAC Collection Station—Birmingham, Alabama

It has been a while since I wrote anything about fungi on this blog so I thought perhaps I should return to these remarkable organisms in another blogpost. As you may have guessed if you are a reader of some of my posts, I really think fungi are an incredible group of organisms. (Yes, I am definitely a fun guy.) I find all of the fungal groups interesting and just down right fun to look at and study. However, my personal bias when it comes to what I think is the most incredible group of fungi is the group called the ascomycetes. Why this group you might ask? It is because of the tremendous diversity of life cycles, growth habits, and habitats of this group of organisms. Perhaps it is also because this was the group of fungi that I studied most extensively in graduate school. What follows is a brief review of fungal taxonomy followed by a brief introduction to this remarkable group of fungi.

Fungal taxonomy follows very specific rules regarding how a given fungus is named and how it is related to other fungi. All true fungi are placed in the Kingdom Fungi. The fungi are then subdivided into smaller and smaller taxa based upon presumed relationships among the members. The largest subgroup is called a division, which is then subdivided into classes, classes are subdivided into orders, then into families, into genera, and finally into species. The fungi grouped into a division have some characteristic(s) that all members of that division share, but which are not found in other fungi. (As an aside, Division is an equivalent term to Phylum). A fungus that produces sexual reproductive spores called ascospores inside of a sac-like structure called an ascus is placed in the Division Ascomycota, common name ascomycetes or the sac fungi. The Ascomycota together with the Basidiomycota form the subkingdom Dikarya. The ascomycetes are a diverse group of fungi in regards to the fruiting bodies they produce that house the asci (plural of ascus). These fruiting bodies range from a single ascus to complex fruiting bodies housing thousands of asci. The fruiting bodies may be open or closed, and vary in shape and color and the substrata on which they grow.

The ascomycetes are particularly important to humans because of the number of antibiotics they produce, their role in the baking and brewing industries, their role in the production of cheese, and the presence of edible members (truffles being perhaps the best known edible ascomycete). Some of the ascomycetes also function as pathogens of humans and this group of fungi are the major cause of diseases of plants. Members of this fungal division also play several important roles in nature: formation of lichens, formation of mycorrhizae, and decomposition of cellulose. Lichens are symbiotic associations between fungi and algae and the majority of lichens have an ascomycete as the fungal symbiont. Some ascomycetes also develop symbiotic associations with certain plant roots, particularly conifers; relationships referred to as mycorrhizae. Mycorrhizae are important to the plants which possess them because they are crucial in the uptake of minerals by the plant roots and the overall health of the plants. The ascomycetes and basidiomycetes are the principal decomposers of cellulose and lignin, components making up plant cell walls. Without these fungal decomposers we would quickly be overrun by a buildup of plant matter in the environment.

In the next blog in this series I will address the diversity of the ascomycete fungi with reference to their fruiting bodies and habitats. Stay tuned!