Tom Volk's Fungus of the Month for January 2004

This month's fungus is Caulorhiza umbonata, the rooting redwood mushroom.

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Caulorhiza umbonata. photo by Dan Czederpiltz-- most of the pseudorhiza was unfortunately cut off

This month's fungus is commonly found fruiting in California during the winter months, especially January. It is just about the only mushroom larger than 2 inches diameter that regularly fruits under coast redwood trees, Sequoia sempervirens. Although it sounds very exotic to collect under redwood trees, this habitat is not very productive in terms of large mushrooms. All the redwoods are only known to be endomycorrhizal with microscopic fungi, and redwood wood is very resistant to decay. Thus it should not be surprising that the widest variety of mushrooms in redwood areas are found in stands of redwood mixed with other trees, such as Douglas fir and tanoak. Both of these species are ectomycorrhizal and decay-prone, and thus support a wide variety of mutualistic, parasitic and saprophytic fungi.

I chose Caulorhiza as FotM to honor my mycology friends in California, who have invited me to visit the past couple of years in January. For a midwestern guy like me, it's a real treat to be able to occasionally collect in California forests and see rather unusual mushrooms. In January 2002 and January 2003, I was fortunate enough to attend weekend mushroom camps of the Sonoma County Mycological Association (SOMA). SOMA signs with me, Darvin Deshazer and Tom SargisTheir mushroom camp is always held the Saturday and Sunday before Martin Luther King holiday in January. They're holding the camp at a new site this year, but unfortunately I won't be able to attend due to previous commitments. I'm likely to attend in 2005. I highly recommend the camp for anyone interested in mushrooms, especially when it's cold and snowy where you live. Besides many organized forays with subsequent display of the collected mushrooms, there are many workshops and lectures. The highlight of the foray may be the fantastic food, provided by gourmet chef Elissa Rubin-Mahon and her crew. Wild mushrooms, such as Boletus edulis, chanterelles, and huitlacoche (corn smut) have been deliciously featured in past years.

Caulorhiza umbonata, about 13 inches (33 cm) from cap to end of root Unlike some of those popular mushrooms, this month's fungus, Caulorhiza umbonata, is not known to be edible, although no poisonings have been reported. It is, however, a fun mushroom to find. The photo to the left shows a large example of a carefully picked fruiting body of Caulorhiza, From the top of the cap to the base of the root-like pseudorhiza in this specimen is about 13 inches, or 33 cm. Almost all of the pseudorhiza-- the rooting part of the stem--was underground. Everything below the arrow was below ground in this specimen. You can clearly see where it starts to appear dirty-- all of that was below ground. In the first picture on this page, unfortunately the pseudorhiza was not completely harvested-- it broke while *someone* was digging it up.

It is unclear what the function of the pseudorhiza might be. We have to assume it must be attached to some part of the substrate, which we assume to be the redwood tree. However, no redwood trees are known to be ectomycorrhizal with members of the Basidiomycota, so this must be either a parasitic or saprophytic relationship. So far as I can figure out, no one knows the exact nature of the relationship of this fungus with redwood trees. It is clear, however, that finding Caulorhiza umbonata is an absolute indicator that a redwood tree is nearby. So if you're walking through the forest, finding this mushroom should help you to locate that elusive redwood tree...

Dan Czederpiltz and Tom Volk with a giant redwoodSpeaking of redwood trees, the photo to the right shows Dan Czederpiltz and I with a very large coast redwood, Sequoia sempervirens. This particular tree is in Big Hendy Grove in Mendocino County, near the Navarro River. The coast redwood is restricted to a fog belt along the coast of California, from southern Monterrey County to just north of the Oregon border. It is an extremely long lived tree (up to 2,200 years) and one of the tallest trees. According to, the record coast redwood tree is 364 feet (110 m) in height and 20 feet (6.1 m) diameter at breast height (dbh, the standard place of measurement for tree width).

Compare the coast redwood with the giant redwood (Sequoiadendron giganteum), also known as the bigtree. Although not as tall (up to 310 ft, or 95 m in height), the giant redwood can have a much larger diameter, up to 35 feet or 11 m dbh. The giant redwood, restricted to about 75 groves in the Sierra Nevada mountains in Northern California, is thus much more massive than its coastal relatives. These include trees you can even drive your car through!

There is a third redwood tree, the dawn redwood (Metasequoia glyptostroboides), the only deciduous member of this group, losing its leaves every fall. This species was described from fossils and was thought to be extinct until a few were found in China. After the Arnold Arboretum at Harvard University sent an expedition to collect seeds, workers in Massachusetts germinated the seeds and generously provided seedling throughout North America and eventually the world. The tree survives very well up through gardening zone 5, and I actually have planted one in my yard here in zone 4, where it's doing very well.

Caulorhiza umbonata was once called Collybia umbonata, but has been separated out because of its rooting base and amyloid spores, as well as some other microscopic characteristics. Another rooting former-Collybia, known as Xerula radicata or Oudemansiella radicata, is separated from both Collybia and Caulorhiza by the presence of skeletal or "sarcodimitic" hyphae-- these are thick walled hyphae without septa, common in the polypores, but unusual for gilled mushrooms. These three genera have been upheld by recent molecular data-- and Collybia has been split into even more genera. You can read more here on this page by Roy Halling called "A revision of Collybia s.l. in the northeastern United States and adjacent Canada." There's a lot to be learned about systematics by looking in the microscope and by grinding up mushrooms!

I hope you enjoyed learning something about the rooting redwood mushroom. It's a beautiful fungus to find, mostly because it means you're in a beautiful area in the winter. I hope you can visit SOMA camp some January and find some.

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

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