The Sac Fungi

diagram showing cross section of a cup fungus, showing asci and ascosporesSac fungi get their names from the fact that they produce their spores, called ascospores, in special pods or sac-like structures called asci (singular ascus). Technically this group of fungi is known as the Ascomycetes or Ascomycota. The drawing at the right shows a cross-section of a cup fungus, a kind of sac fungus, and the microsopic view shows how asci cover the inside of the cup. The orange color is just to serve as a background. You might want to compare this diagram showing asci and ascospores with the diagram showing basidia and basidiospores on the club fungus page.

Morel Mushroom, Morchella angusticepsOne of the most famous sac fungi is the Morel mushroom shown at the right. Morels are famous because they are so good to eat! Common in many parts of North America, they grow in rich soil and though there are several species (this one is Morchella angusticeps), they are all delicious.

There are some "false morels," which are not so good for eating. However, any mushroom with a honeycombed cap like the one at the right, in which the depressions are very deep, is a morel. The depressions in false morels are shallow or nonexistent. Spore-producing sacs, or asci, are borne in palisadelike layers lining the cap's depressions.

Anthracnose Disease

Dogwood anthracnoseRight now a terrible disease is spreading through eastern North America killing Flowering Dogwoods, one of our most beautiful and treasured native tree species. The disease is caused by Dogwood Anthracnose Fungus, and the picture at the left shows the disease's symptoms. Note the dark brown spots (dead tissue) surrounded by yellowness. In the disease's later stages the leaves are often red, as during the fall. The fungus kills by releasing a substance that breaks down the dogwoods' tissues into something the fungus can absorb and use for its own purposes. The fungus also releases toxins that kill tissue outright, and can spread into the stem to infect new limbs and cause cankers. There are two main types of anthracnose fungus on dogwoods. One is a species of Discula, to which science hasn't yet given a scientific name.. The other, more deadly, fungus is called Discula destructiva. Since this disease is so important, there is plenty on the Web about it. To visit one of the best sites, which has a good section on identifying fungi by looking at their DNA, click here.

Powdery Mildew

Dogwood Powdery MildewAt the left you more Flowering Dogwood leaves, this time very sick with a completely different kind of fungal disease. You can see that the newly developed spring leaves are pale, puckery, and appear to be covered with a white dust or powder. The close-up at the lower right shows that there's not much to this white stuff -- it really is like powder. That powder is the fungus and this species doesn't get much more glamorous-looking than that. The fungus is causing Dogwood Powdery Mildew, and the genus name for it is either Microsphaera or Phyllactinia.

The white matter you see consists of masses of tangled hyphae that obtain their food by sending rootlike haustoria into the leaf's living cells. At this early stage in the mildew's lifecycle it is reproducing with special kinds of asexual spores called conidia. This species can reproduce when the tips of certain vegetative hyphae simply constrict in certain places (no sex involved) forming egg-shaped spores that then can blow away and under proper conditions sprout new hyphae. Later in the year sexual reproductive structures will form in the powdery area (tiny items barely large enough to see with the naked eye) and they will produce regular sex-based spores.

Blue-green Molds

Penicillium on grapesThe table grapes at the right, which had been stored for too long in a refrigerator, is a species of the genus Penicillium. This is the same genus from which the powerful antibiotic penicillin is derived. If you ever opened an old jar of jelly or jam and its surface was covered with a greenish mat, that was probably Penicillium, too. In case you don't like to throw food away you will be happy to know that when you find Penicillium covering your favorite jam, the fungus itself is not poisonous and if the mold layer is removed the food will still be edible, assuming that something else hasn't spoiled it. Another big genus among the blue-green molds is Aspergillus, whose species aren't always so generous. They can cause ear and lung infections.

XylariaThe black-and-white little fungus at the right (only 0.4 inch or 10 mm high) is a sac fungus of the genus Xylaria, growing on the wood of a log fallen in the woods. Most people would never notice this little being unless they were specifically looking for small things, poking around on fallen logs. This species isn't illustrated in most mushroom field guides. In fact, I can't even find a common English name for it.

You may be more familiar with other sac fungi, at least their names. For example you have probably heard of yeast and maybe ergots. I'm looking for pictures of these and other sac fungi, so stay tuned...

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