Sac Fungi

When we think of fungi, we mostly think of mushrooms. All mushrooms are fungi, but not all fungi are mushrooms. One type of gourmet “mushroom” called a morel does not actually look like the pedestal-shaped mushroom that we are familiar with. Unlike button mushrooms, which belong to the Basidiomycota phylum of fungi, morels are a type of sac fungi. Sac fungi, or ascomycetes, named for their phylum Ascomycota, is a group of fungi consisting of around 30,000 species. They are sapotrophs which play an important ecological role by decomposing resistant materials containing cellulose, lignin, or collagen.

In sac fungi, their phylum name refers to the ascus (from the Greek askos, meaning bag or sac) which is a finger-like sac that develops during sexual reproduction. The asci are usually surrounded and protected by sterile hyphae within a fruiting body called an ascocarp. A fruiting body is a structure where spores are produced and released.

Ascomycete Shapes

Ascocarps come in many shapes. In molds, they are shaped like flasks. In cup fungi, they are cup shaped. In morels, the ascocarps are long stalks crowned by a bell-shaped hood of convoluted tissue. The asci become swollen as they mature in most sac fungi, and burst when ripe to expel the windblown spores.

Types of Sac Fungi

There are around 30,000 different species of ascomycetes, and all fill an important ecological role in breaking down tough material. However, different ascomycetes go about their work in somewhat different ways. Red bread molds, e.g. Neurospora, cup fungi, morels, and truffles are all sac fungi. Morels and truffles are highly prized gourmet delicacies, made all the more valuable due to the fact that no one has been able to successfully cultivate them; all morels and truffles are collected from the wild. Many sac fungi are parasitic and grow on plants. Leaf curl fungi, such as peach leaf curl, and powdery mildews grow on the leaves of the infected plant. Chestnut blight and Dutch elm disease strike at chestnut trees and Dutch elm trees respectively. Ergot infects rye, and, less commonly, other grains. Many of the organisms referred to as yeasts are also ascomycetes. Saccharomyces cerevisiae, or brewer’s yeast, is one such example of a sac fungi that serves a human economic function. Other yeasts serve a different human function through genetic engineering. When an experiment requires the use of a eukaryote, instead of the usual E. coli, which is a prokaryote and would function differently than a eukaryote, yeasts can be used to provide an accurate result.