Split Gill—Schizophyllum commune

© Else Vellinga, Ph.D.
Lab
Original publication: Mycena News, May 2013

Throughout the winter white and hairy split gill fruitbodies (Schizophyllum commune) lined my route through Berkeley—these fungi were holding out in open places on stumps and dead branches, despite the record dry weather. During rain showers they opened up and were soft, pliable and more colorful—only to turn back to their hard and white stage when the sun came out again (figs 1 & 2). They deserve a second look, especially their gills, because these are unique among mushrooms! The gills are split on the tips and the edges curl outwards; that is obviously where the common name comes from.

Buller, a mycologist who was a keen observer of everything that has to do with spore production and dispersal, found out that even after two years of drought, a split gill fruitbody would spring back to life and start forming spores again when wetted. Sixteen years, however, was too long a period to get going again. He also showed clearly (see fig. 3) that in drought, the lamellae roll up and cover the underside effectively. In wet weather, when the conditions for spore germination are ideal, they straighten out. Then the hymenium, where the spores are formed, is exposed and offspring can be sent out into the world.

Split gills are the only fungi with this mechanism, and the anatomy of their fruitbodies is different from all other gilled mushrooms. Basically, they are formed by a fusion of several separate, smooth-surfaced, up-side-down cups in which, secondarily, the gills are formed. But these gills are not of the same type of tissue as in your Amanita. In the grand scheme of mushrooms, split gill belongs to the order Agaricales; the order to which most gilled mushrooms belong. But they form a special group, together with the beefsteak fungus, Fistulina—also composed of little separate fruiting bodies embedded in that delicious, succulent fruiting body.


Fig. 3. Cross sections through wet and dry fruitbodies of Schizophyllum commune
(from Buller, 1909)

Schizophyllum is one of the very few species of mushrooms that can be found all over the world–wherever its substrate (dead wood) is available. All specimens, from whatever part of the world they come, can still mate with each other. However, this does not mean that individual spores travel long distances. An experiment in the Caribbean showed that the North American strains did not reach Puerto Rico, whereas the South American spores made it to Florida. And just as in humans, there are genetic differences among specimens from the different continents, resulting in three major groupings in Schizophyllum commune: a North American group, a South American group, and an eastern hemisphere group to which the specimens from Europe, Asia and Africa belong. But, recent movements of people have changed this neat pattern a bit—our Californian split gills can either be originally North American, or belong to the eastern hemisphere group.

The split gill is very common in the Bay area—growing on dead wood, and causing white rot (it devours lignin and cellulose leaving white, stringy matter behind). But it is not very picky in its substrate. In Ireland and Great Britain it likes bales of hay and straw that are covered in big plastic bags. This spells bad luck for the farmer as the fungus devours the hay, and the little hay that is left is shunned by the cattle.

There are also reports of this species being found in humans and other animals. A report on a big lump, completely made up of split gill hyphae, on the neck of a dog did not make for nice reading (no, the dog did not survive), nor is reading about mushrooms formed in the sinuses of a little girl very appetizing. It is not clear from these reports how the fungus got into the animal or human, and what exactly it lives on. But it is clear that this fungus is an opportunistic pathogen in mammals, especially the vulnerable (very young and very old) and those people whose immune systems are not working well.

On the other hand, Schizophyllum is eaten in many tropical regions and even collected in quantities and sold in roadside stalls and markets. Here is one recipe from the Upper-Shaba region in Congo where it is called sepa: “The natives boil the mushrooms for a long time in water to which a vegetable salt, rich in potassium, has been added; this has an effect of tenderizing. After one or two hours of cooking, the drained mushrooms are mixed with sifted peanuts, seasoned with a little salt and a final addition of oil. Prepared in this way, the mushrooms are eaten with bukari (the principal starchy dish of the region).”

Schizophyllum is also the ideal fungal rat lab—it grows well and easily forms fruitbodies in culture. So, its sex life is well known and has turned out to be very complicated. Hydrophobic proteins—so instrumental in making fruitbodies—were discovered in this fungus for the first time. Its complete ge­nome has been sequenced as well, showing the specific enzymatic machinery needed to degrade wood, all the genes involved in the forming of fruitbodies and those genes which are so important in mating and mate recognition. In short, this is a versatile, fascinating fungus with humble and inconspicuous fruitbodies.

Some literature on Schizophyllum commune

Else Vellinga, Ph.D., is interested in mushroom taxonomy and has been studying mushrooms in California and beyond for years. A frequent contributor to Mycena News, she is also fascinated by interactions between fungi and other organisms. In her free time she knits, and knits, and knits!