The Fungus Kingdom is often but not always divided into seven phyla (sometimes called divisions -- see our "Pigeon-Holing" page), as shown at the right.
If you look into books a few years old, a different breakdown will be given, and different words used. The understanding of what fungi are and how they are related to one another is constantly changing. If you are really serious about having access to the most recent information, check out a page called "Kingdoms, Classification and Biodiversity" focusing on the fungi.
Below is a little information about the main phyla of fungi we might find and recognize in our backyards:
Most but by no means all of the most interesting fungi we find in our neighborhoods are in this phylum. As the accompanying drawing indicates, in this group, spores-- more technically known as basidiospores -- are produced on microscopic, club-like structures called basidia (singular basidium).
Basidia cover part of the fungus's reproductive structures. In gilled mushrooms the gills are covered with them. The above diagram shows a cross section of such a gill. Basidospores detach from the basidia and drift down out of the gills, and then are dispersed on wind currents. Basidia occur elsewhere on the fruiting bodies of non-gilled fungi. You might want to compare the above diagram showing basidia and basidiospores with the diagrams below.
The above describes sexual reproduction. Members of the Basidiomycota also can reproduce asexually, though it is not as common here as among the next two phyla. This is accomplished when fragments of the fungus break off and the fragment hyphae simply continue growing in the manner of the parent fungus. Basidiomycota hyphae can also produce arm-like structures at the end of which appear tiny, single-celled, ±spherical items called conidia. Conidia behave like the first cell of a new hypha. It simply grows until a new hypha is formed, and then that hypha can produce more conidia, all without sex having ever taken place.
Good things to remember about members of the Basidiomycota are:
- spores produced during sexual reproduction are created in microscopic, club-shaped basidium, which, in the case of gilled mushrooms, appear on the gills
- cross walls (septa) in hyphae separate cell nuclei
- the sexual stage involves the production of basidiospores in basidia
The Ascomycota ("Sac Fungi")
In the old days these were called "sac fungi" because they produce their spores, called ascospores, in special pods or sac-like structures called asci (singular ascus). The drawing at the right shows a cross-section of a cup fungus, a kind of sac fungus, and the microscopic view shows how asci cover the inside of the cup. The orange color is just to serve as a background.
Members of the Ascomycota also can reproduce asexually, producing conidia as described for the Basidiomycota.
Good things to remember about members of the Ascomycota are:
- spores produced during sexual reproduction are created in microscopic, club-shaped asci, which may appear on fruiting bodies of many shapes
- cross walls (septa) in hyphae separate cell nuclei
- the sexual stage involves the production of ascospores in asci
The Zygomycota ("Conjugation Fungi")
The old name, "Conjugation fungi" was always sort of a clumsy name for this group. The name reflects the fact that among these fungi, instead of the sexual spores being produced on conspicuous spore-producing bodies such as mushrooms or cups, they are produced in very small structures that form when the fungal hyphae "come into conjunction," or meet one another. The above diagram shows what happens. Two hyphae of different mating strains "come into conjunction," bulges form on each of them (the progametangia), and this leads to the mature "zygospore," which accounts for the name of the division.
These zygospores can be thought of as resting stages, since they often form when conditions get difficult -- maybe because its environment is drying out -- for the hyphae to keep growing. The hyphae may then wither and die, but the tough zygospores will "rest" until good growing conditions return. Then the zygospores germinate (That's when meiosis occurs), and new hyphae are formed. These new hyphae may then reproduce asexually for a long time, producing sporangia which break open releasing spores that germinate to produce new hyphae -- all without the sexual process ever taking place! But then if things dry out, the hyphae will start producing zygospore "resting stages" again.
Something important to notice in the above diagram is that the dots, which represent cell nuclei, are not separated from one another by cell walls! Therefore, good things to remember about members of the Zygomycota are:
- they don't form conspicuous fruiting bodies
- no cross walls separate cell nuclei
- the sexual stage involves the creation of zygospores
The diagram above shows how zygospores are produced through a sexual process. Conjugation fungi can also reproduce without sex being involved (asexually) to produce just plain spores.
The Fungi Imperfecti ("Imperfect Fungi," sometimes known as the Deuteromycota")
Some specialists would insist that the Fungi Imperfecti are not a real phylum at all, but rather just an artificial grouping of fungi of various kinds that are not well understood, and there's something to that argument.
In fact, the name "Imperfect Fungi" comes about not because the fungi are imperfect in any way, but because science understands their life cycles "imperfectly." Mainly, no one has yet figured out how they reproduce sexually, if they reproduce sexually at all. And a lot of them may never reproduce sexually! They would reproduce entirely by such agencies as the fragmentation and conidia production described above. Most Imperfect Fungi look as if they probably belong to the Ascomycota.
Around my trailer in southwestern Mississippi the most common tree is the Sweetgum. It happens that nearly every leaf on every Sweetgum tree as I write these words is infected by the "leafspot fungus" shown at the right -- and every year the same leaf disease strikes. The fungal disease, probably Gloeosporium nervisequum, is a kind of filamentous fungus and it's an "imperfect" one. As summer progresses the reddish spots enlarge and eventually turn black, making the leaf look not nearly as pretty as it does in this picture.
I think it's pretty neat that science doesn't really know whether such a common species right outside my window has a means of reproducing sexually or not!