The fungi can be divided into three basic forms based on their basic morphology and reproductive structures. Fungi did not evolve to suit the need for humans to neatly classify things, so some species may not fit well into these arbitrary categories, and in some cases, a species may exhibit characteristics of all three at some point. It is important to remember that these categories do not necessarily reflect evolutionary relationships -- they are just convenient terms used to describe and talk about fungi.
Yeasts
Yeasts are fungi characterized by a mostly unicellular growth form, although chains or clusters of cells can arise in which new cells are budded off from mother cells. There are many species of yeasts, the most well known being Saccharomyces cerevisiae, the common baker’s and brewer’s yeast. Much of what we know about cell and molecular biology has come from studying this yeast. A strain of Saccharomyces is what you get when you buy a package of dried yeast at a grocery store.
Some fungal species are dimorphic, which means they can switch between a hyphal and yeast growth form. Which form the fungus takes depends on environmental conditions, such as how much and what kinds of nutrients are available, temperature, pH, or other factors.
Molds
Mold is a general term given to fungi growing as a mycelium that generates large numbers of conidia (or sometimes sexual spores). These spores are often brightly colored, giving the mycelium a distinctive appearance that may be useful in identifying the species.
Some common mold genera are Penicillium, Aspergillus, and Rhizopus. Many early advancements in our understanding of genetics came from work with the mold Neurospora crassa. Both Aspergillus and Neurospora are still extensively studied in laboratories around the world.
Mushrooms
For most people, mushrooms are the most commonly encountered and recognized fungi. When you observe a mushroom you are seeing a structure specialized for sexual reproduction. Most of the fungus remains unseen, attached to the mushroom underground or in the wood from which the mushroom grows.
Some mycologists claim that mushrooms are only formed by Basidiomycetes, which produce the typical stem (stipe), and cap (pileus) with gills (lamellae) or pores on the underside. However, most people are content to consider other forms, such as the morel, which is an Ascomycete and does not have a typical-looking cap or gills, to be mushrooms as well.
Some popular commercially grown edible or medicinal mushrooms include Agaricus bisporis and relatives (the button mushroom), Pleurotus ostreatus (oyster), and Lentinula edodes (shiitake) among others.
Philip McIntosh - The author holds a B.Sc. in Botany and Chemistry and an M.A in Biology and he has thirty + years of experience in science and industry.
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