Introduction to the Fungi
In this part of the course, we will be studying the organisms that are referred to as fungi (sing.=fungus). Although you have now studied various groups of plants and algae, as well as other eukaryotic organisms, in other courses, you will find that the fungi are probably the least understood among the eukaryotes. Looking back at my undergraduate career, prior to taking my first mycology class, I had a very negative concept of the fungi. My impression of fungi was that they were disease-causing organisms that were found in unsanitary conditions. Although this impression was not entirely wrong, fungi are so much more than that. They are also very beneficial organisms. We have derived a number of useful antibiotics from them, including the "wonder drug" penicillin. Without fungi, we would not have leavened bread, Roquefort and Camembert cheeses, beer, wine and other alcoholic beverages and some mushrooms, morels and truffles are considered to be delicacies among gourmands. While these aspects of fungi are of interest, they will not be the emphasis on our discussions of fungi. If you are interested in learning about these aspects of fungi, you may go to the Botany 135 home page. The emphasis here, instead, will be to study the relationships of the various groups of fungi and attempt to make sense of their phylogeny.
Classification of Fungi
Once upon a time biologist only recognized two kingdoms: Plant and Animal (this was how organisms were classified when I was an undergraduate). Fungi, as well as bacteria and algae were classified in the plant kingdom under this system and that is the reason that these organisms are traditionally studied in botany. In the case of fungi, MYCOLOGY is that part of botany that studies fungi. Although fungi are no longer classified as plants, there is still good reason to study them in botany. Fungi are most often associated with plants, commonly as decomposers, and pathogens, and as their benefactors, e.g. mycorrhiza, but "What is a fungus?" Based on what your studies on plants, in this course, you know that plants are known to be derived from a single algal ancestor from the algal division: Chlorophyta, i.e. they are monophyletic. Once upon a time, the fungi were also believed to be monophyletic and to be derived from an algal ancestor that lost its ability to photosynthesize. However, over time, with the discovery of new techniques in determining relationships between organisms, it was discovered that the fungi are made up of a polyphyletic group of organisms that, in some cases, are very distantly related to one another. Thus, organisms that we call fungi are not grouped together because they are closely related, but rather because they share a combination of characteristics that we will now go over:
Characteristics of "fung" in the broad sense
In summary then, the organisms that we call fungi represent a heterogenous group, i.e., they are polyphyletic, that are not closely related as you will soon see.
When I was an undergraduate, organisms that were defined as fungi were heterotrophs, with cell walls, that have filamentous or yeast thalli. Today, fungi that are classified in the Kingdom Mycetae (=true fungi), have a more restrictive set of characteristics: Eukaryotes with cell wall material composed primarily of chitin and derive their nutrition by absorption. Why the change? As with any science discipline, knowledge in mycology is dynamic and we have accumulated a great deal of knowledge about the fungi since I first took mycology 30 years ago. The additional knowledge has led us to change our concepts as to the relationship of those organisms that were classified as fungi. Much of the knowledge that led to these changes began in the early 1960ís, when a great deal of research was carried out in fungal ultrastructure. This was later followed by comparative studies on cell wall biochemistry (Barnicki-Garcia, 1970) and more recently molecular approaches, utilized in studying relationships of organisms, has led to further changes in our concepts as to how we define fungi.
Another change that occurred during this period of time that affected not only fungi, but also "plants" and "animals" as well. When I was an undergraduate, the classification for plants and animals were very broadly defined. As I mentioned, above, organisms in those days were classified as either plants or animals. Fungi, as well as bacteria and algae were classified in the plant kingdom, based mainly on the presence of a cell wall and the lack of ingestion of food material. However, *Whittaker (1969) erected the five-kingdom system, which is currently still the accepted system of classification of organisms. As a result, the fungi, algae and bacteria were placed in different kingdoms. While, the concepts of the five kingdoms have changed since Whittaker (1969), the classification of organisms into five kingdoms have persisted.
Although, our definition of a fungus has changed a great deal, by tradition, mycology classes have continued to study the same organisms that have been studied since the 1960ís and earlier. While mycologists have learned a great deal about the fungi in these last 30-35 years, there is still not agreement as to how best to classify the fungi, nor will there likely be any agreement at a later time. Some examples of the more popular classification schemes are reproduced below:
|Ainsworth and Bisby (1971)||Bessey (1950)||Alexopoulos (1962)|
|Kingdom Fungi||Kingdom Plantae
Over the last ten years, there have a great deal of changes in the concepts of the relationships of the various groups of fungi. The classification below represents one of the more recent systems and is based, in part, on molecular research that has been carried out in recent years. Because of time constraints, not all of the different taxa of "fungi" will be listed below or covered in this course.
Division: Myxomycota (Currently classified with protozoans)
The above two divisions have also been placed in a recently erected Kingdom: Stramenopila. This kingdom includes the divisions Phaeophyta and Chrysophyta, which you have already studied in the algae portion of this course
Kingdom: Myceteae (=Fungi)
Division: "Deuteromycota" (Asexual Fungi)
As we study the various groups of fungi, I will attempt to point out the problems in using a classification scheme in a course such as this one where the goal is to study the phylogeny and relationship of the various organisms that we are calling fungi.
During the final lab in this section of the course, I will bring in several dated textbooks, such as Alexoupolous (1962) and Bessey (1950), which were considered outstanding textbooks for their time. At that time, I want you to compare the concepts of fungi in these books with our present concept. Whenever I look back at these textbooks, it never ceases to amaze me as to how much we have progressed in our knowledge of the fungi. Perhaps, this will also be something that you will appreciate by the end of this section of the course.
*Whittaker, R.H. 1969. New concepts of kingdoms of organisms. Science 163: 150-161.