German pretzel girlyummy dextrorotatory pretzelTom Volk's Fungus of the Month for October 2003

another yummy dextrorotatory pretzelThis month's fungus, in honor of Oktoberfest, is Hemitrichia serpula, the pretzel slime mold.

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Hemitrichia serpula, the pretzel slime mold Although this month's fungus is not salty, its twisted reproductive structures resemble the delicious German pretzels found at every Oktoberfest. You may not know it, but La Crosse, Wisconsin (where I live) is home to one of the largest Oktoberfest celebrations in North America. You can read for more information on the yearly celebration in La Crosse, which has been happening every year since 1961. USA Today has rated it one of the Top 10 Oktoberfest celebrations in all the world. I hope you can visit some day.

This month's fungus is not a fungus at all, but a slime mold in the phylum Myxomycota in the kingdom Protista. If you've been reading my pages, you already know about Hemitrichia's larger relative Fuligo septica, the dog vomit slime mold. These slime molds were at one time considered to be fungi and have been traditionally been studied by mycologists, so it is perfectly within the realm of mycology to have a slime mold as the Fungus of the Month-- at least as an honorary FotM. Slime molds do not fit at all into the kingdom Fungi, because they lack cell walls, lack exoenzymes (they engulf bacteria in much the same way amoebae do), and lack many other fungal characteristics. They have been traditionally studied by mycologists because their small, delicate fruiting bodies tend to be fungal in appearance. Most slime mold fruiting bodies are really quite beautiful, especially if you look at them at higher magnification, like under a dissecting microscope with a powerful light. They can also be spectacular under a regular light microscope, as you'll see later.

A=Dictydium cancellatum, B=Diachea brilbrilosa, (both sporangia, pix by Nik Zitomer) C=Lycogala epidendrum (aethallia), D=Hemitrichia serpula (plasmodiocarp)There are three major types of slime mold fruiting bodies

Slime molds are usually found on old well-rotted logs in shaded forests, because there they can find the moisture and bacteria required for survival.

The fruiting bodies produce spores, which can germinate to form myxamoebae or flagellated swarm cells. These later fuse to form the plasmodium, which later forms the fruiting body. Most of the fruiting bodies are only a millimeter or two in height so it does take some searching to find them. They are actually very common if you take the time to look-- once you start finding them, you'll agree that it's well worth the time and effort, especially if you have a hand lens or a dissecting microscope. Their beauty is amazing.

I have some more online images of slime molds here. For more information on slime molds including a world-wide directory of people who study slime molds, please visit MyxoWeb, created and maintained by Denise Binion.

When you're looking closely, you may find a couple of stages of the life cycle, the reproductive part and the vegetative (feeding) part. I've already talked about the fruiting body above. Prior to fruiting, the vegetative phase of the slime molds takes the form of a plasmodium, essentially a large amoeba.

phaneroplasmodium of a slime moldThere are three types of plasmodia:

Hemitrichia serpula capillitium and sporesIf you look closely at the fruiting body of Hemitrichia, you can see some fuzzy stuff coming from the plasmodiocarp. If you mount a bit of this fuzz, you'll see some spores embedded in a matrix of threads called the capillitium. The capillitium is often heavily ornamented, and in Hemitrichia it looks kind of like a hemp rope. The capillitium is made of lime (calcium carbonate), which makes its beauty even more amazing. The capillitium of a slime mold is thought to function as a time-release mechanism for the spores, holding them in so that they are released more slowly. Compare this to one of those scrubbers you keep in your kitchen sink-- you scrub your dishes and little bits of food get caught in it. These little pieces of food, like the spores of a slime mold, eventually get washed or blown out over a long period of time. It's probably the slime mold's way of hedging its bets about when the best time for spore release might be.
logo for Oktoberfest in La Crosse, 2003

I hope you've enjoyed reading about Hemitrichia serpula and other slime molds. Maybe this might inspire you to take a closer look at this fascinating and beautiful group of organisms. Or maybe it will just inspire you to visit an Oktoberfest celebration near you-- or even come to visit La Crosse for our Oktoberfest. I hope you can visit someday.

If you have anything to add, or if you have corrections, comments, or recommendations for future FotM's (or maybe you'd like to be co-author of a FotM?), please write to me at

This page and other pages are © Copyright 2003 by Thomas J. Volk, University of Wisconsin-La Crosse.

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