The Fungus Kingdom is often but not always divided into five 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 might 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 divisions of fungi we might find and recognize in our backyards: The Basidiomycota ("Club Fungi") 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, ąspherical 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:
The Ascomycota ("Sac
Fungi") 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:
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:
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 Glomeromycota") 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.
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! |
Most but by no
means all of the most interesting fungi we find in our neighborhoods are
in this phylum. As the drawing at the right indicates, in this group
spores, more technically known as basidiospores,
are produced on microscopic, club-like structures called
basidia (singular basidium).
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. 
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.