sulphur shelt
Sulphur Shelf Mushroom

October 15, 2019

What kind of organism is a fungus? Certainly not a plant, although until recently even scientists believed that was the case.   However, most fungi build their cell walls out of chitin, the same material as the hard outer shells of insects, and plants do not make chitin.   Now it has been determined that they are more closely related to animals, and have been placed in their own Kingdom.  The body of the fungus is made up of a web of microscopic filaments that are buried in the soil, in wood, or in another food source.   These webs live on and grow unseen until they develop mushrooms, puffballs, truffles, brackets, cups, “birds nests,” “corals” or other fruiting bodies.

The fruiting bodies often seem to sprout up overnight. They can do this because when they begin to enlarge they already contain their full complement of structural cells. It requires only a heavy rain to fall, at which time the fungus body pumps water into these cells, and almost overnight some mushrooms can go from pin-head size to full size.

Generally, we avoid picking the numerous mushrooms we find along our hiking trails as we don’t have the expertise to be confident in identifying the edible varieties. Two exceptions are the morel and the sulfur shelf.   Most Wisconsinites are familiar with the morel, but unless you frequent the woods you may not have seen a sulfur shelf.   This large fungus, which is also known as “chicken-of-the-woods”, announces its presence with a bright orange top and gorgeous sulfur yellow underside.  Called a bracket or shelf mushroom because of the way it extends from a tree trunk, the sulfur shelf is often found on or around an oak tree and often comes back year after year.   One year, we discovered a huge specimen growing in the farmyard on our old willow.

Young sulfurs are moist, rubbery, and easily broken, while more mature specimens become pale, tough, and are often dotted with insect holes. Many think that the texture and even flavor is reminiscent of chicken, but those who would like to try it should be aware that, as with any mushroom, some individuals have a bad reaction, including light-headedness and nausea. "The neat thing is that it is impossible to misidentify," said Greg Mueller, curator of mycology at Chicago’s Field Museum. "It's the only big, bright orange bracket mushroom with sulfur pores growing on wood out there." This was pretty much the accepted wisdom well into the 1980′s, but as allergic reactions seemed to become more numerous, it was found that specimens growing on certain trees and in certain areas sometimes did cause problems and gastric distress. Eucalyptus, evergreens, and locust in particular were suspect and the advice now given is to avoid any sulfurs collected from these trees.

The sulfur shelf grows in large flattened fans that lie in horizontal tiers, sometimes becoming huge and weighing as much as a hundred pounds. It is more accurately called a polypore because, rather than having gills underneath its cap like many other mushrooms, it has tubes, or pores -- tiny holes dotting the underside. These are lined with spore-producing organs, as fungi must produce enormous numbers of spores so that at least a few will land on favorable surfaces for germination.

All polypores have two or three kinds of cells -- the rapidly expanding inflatable generative cells, along with two kinds of reinforcing cells, referred to as ‘binding’ or ‘skeletal’. The hard woody conks you see on trees have all three and will persist on their hosts for several years. The sulfur shelf has but two -- the quickly expanding (and edible) generative type, and the more rigid, slower growing binding kind. These latter cells give the fruiting body strength and rigidity and can even hold it together for a time after the softer tissue dries out and collapses.

The sulfur fungus may grow inside a tree for some 50 years in order to build up enough energy to form the colorful fruiting bodies, and during that time it is feeding upon the tree's inner tissues, causing decay. All wood is composed mostly of two substances -- cellulose which is white and forms the primary wall of all plant cells, and lignin which makes up the brown inner wall in some cells, especially those of trees.

Polypores, such as the sulfur shelf, harbor both brown rot fungi that degrade only the white cellulose leaving the brown lignin to crumble to dust, and white rot fungi that decompose the lignin and leave the white stringy cellulose behind. As the decay proceeds, hollows are created that house all sorts of creatures, and eventually the fungi will accomplish the transformation of the tree into soil.

Meanwhile, springtails, nematodes, and other tiny beings graze on the fungi inside the tree, while fungus gnats, fungus flies, pill bugs, and various fungus beetles feed on the shelf fungus itself and are in turn picked off by birds. These fungi play an important role in the health and vigor of the forest but harvesting their fruits will cause no harm, and we can enjoy discovering the eye-catching color amidst all the green, and have it for supper, as well.