Tom Volk's Fungus of the Month for August 2003

This month's fungus is Hydnellum caeruleum, the blue and orange Hydnellum

--by Sean Westmoreland and Tom Volk

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Sean Westmoreland with masses of Hydnellum caeruleum in Michigan.  photo by Nik ZitomerThis month's fungus is the favorite of this month's coauthor, Sean Westmoreland. Sean has completed his Master's of Science degree at the University of Wisconsin-La Crosse in April of 2003 with his thesis entitled "Morphological and molecular studies in Hydnellum (Basidiomycota, Thelephoraceae), reinforced with a new method, Chemosystematics with HPLC using Mass Spectroscopy (CHUMS)." Much of this page is modified from his thesis. Congratulations to Sean!

Hydnellum is a very interesting genus with very unusual fruiting bodies. At least you might consider them unusual if you're used to only looking at mushroom-like fruiting bodies. Hydnellum fruiting bodies are distinguished by their indeterminate growth habit (they can engulf twigs and leaves) and, to bear their basidiospores, they have teeth on the underside instead of gills or pores. They are mycorrhizal and also have dark tuberculate or warted spores, which puts them in the family Thelephoraceae. This makes their closest relatives Thelephora, Tomentella, and Sarcodon. Hydnellum also can be grouped morphologically into a loose assemblage of fungi called the "stipitate hydnums," toothed fungi with stems. At this point it would help you to know about all the tooth fungi and how they are classified.

H. caeruleum from Sweden, courtesy of Monica Svensson But first we'll take a look at the most beautiful photo of a Hydnellum caeruleum I have ever seen. The photo to the right is from Monica Svensson, InforMedia Bollnaes, Sweden. You can visit her site, InforMedia Svamping, in Swedish, English, and French. Coincidentally, she sent us this picture one day before we started working on Hydnellum caeruleum as FotM. Thanks to Monica!

Introduction to toothed fungi.

Within the kingdom Fungi, groups of species form a variety of structures to disperse their spores. Certain groups may only reproduce asexually, like the molds, and others reproduce sexually, like gilled mushrooms. The gilled mushrooms belong to the phylum Basidiomycota and produce their spores on basidia, which are club-shaped structures that can be found lining the hymenophore (spore-bearing surface). Within the Basidiomycota, the mushroom (fruiting body) most often produces gills to bear the basidia, but there are a wide variety of other ways the surface area is increased, like pores, folds, or even in sacs. There are a variety of fruiting bodies that even produce teeth, ranging from flat crust-like fruiting bodies to mushroom-like structures to gelatinous jelly-like fruiting bodies. Although almost all toothed fungi were once placed in the genus Hydnum based on this one hymenophore character, modern systematics now recognizes many genera, at least 37 in at least 13 families. You can see a list of the ones we've come up with here. These genera take many forms, such as resupinate, reflexed, mushroom-like, conks, coral-like, and even composed of nothing but teeth, as in Hericium.

We are particularly interested in the toothed mushrooms that have a stem (stipe) and grow on the ground. These mushrooms have collectively been called the stipitate hydnums (stipitate = having a stem, hydnum = fungus with teeth). All of the stipitate hydnums are believed to be ectomycorrhizal with photosynthetic trees. They receive nutrients from the trees and in return help the plants absorb water and minerals. Without this association, most trees would not survive or be as successful.

Most mycologists (us included) recognize the following five genera of stipitate hydnums, which belong in three families: Bankera, Phellodon, Sarcodon, Hydnum, and Hydnellum. For identification, these genera are initially separated based on spore color. Bankera, Hydnum, and Phellodon produce white spores, while Sarcodon and Hydnellum produce brown spores. Bankera, Hydnum, and Phellodon are separated based on context and spore ornamentation. Bankera and Hydnum both have a fleshy context, while the others are leathery. Bankera has tuberculate or echinulate spores, while Hydnum has smooth spores. Phellodon has a tough context and echinulate spores. Hydnellum can be separated from Sarcodon by Hydnellum's fibrous, zonate context. Hydnellum also has an indeterminate growth habit that can be seen in fruiting bodies that engulf twigs and needles, while Sarcodon has a determinate growth habit.

Flowchart to identify genera of stipitate hydnums

Susan Hopkins with wool dyed with fungi H. caeruleum pigmentsHydnellum species and other fungi are often used to dye wool, as shown to the left with Susan Hopkins, dyer extraordinaire from New Jersey. It's really fun to dye wool with fungi. You can read more about the process and the very enthusiastic dyers on this page on Dermocybe semisanguineus and this page on Pisolithus tinctorius Hydnellum species, in particular, contain a number of interesting pigments. For example, H. caeruleum contains aurantiacin and thelephoric acid. Some of these colors can be seen in the fruiting bodies to the right. The top one is oozing aurantiacin, and the bottom one shows many colors within the longitudinal section of a fruiting body.

Because Hydnellum species have been used for centuries in dyeing silk and wool, we wanted to see if we could use differences in pigment production to help distinguish the different species. There have been other mycologists (Hall, Sullivan, Baird) that have used the presence of absence of pigments to help distinguish the different Hydnellum species. When looking just at pigment production, we found that our data reflected past studies. So we decided to exploit the chemical differences between Hydnellum species in a different way using high performance liquid chromatography (HPLC) and mass spectroscopy. None of this is published yet, so you just get to read the abstract to Sean's M.S. thesis:

"Hydnellum is a genus of stipitate hydnaceous fungi that can be recognized by their brown, ornamented basidiospores, leathery texture, and indeterminate, mycorrhizal growth habit. Although previous taxonomic works have been useful, there are many disagreements between authors as to the correct delimitation and placement of Hydnellum species. An extensive historical literature review of the toothed fungi, beginning in 1753, is incorporated, necessitating translation of Latin and French descriptions. Since there are discrepancies in the literature about proper classification and because of only limited recent work on Hydnellum, a re-examination of the species with modern taxonomic methods is warranted. We have undertaken morphological, molecular (DNA sequencing), and chemical (pigment) studies of Hydnellum species. Eighty-seven collections were examined morphologically, and 36 of those collections were analyzed by comparing ITS sequences. Fifteen collections were studied with CHUMS, chemosystematics with high performance liquid chromatography (HPLC) using mass spectroscopy. This method compares species using the presence or absence of chemical compounds to determine relatedness. A total of 54 compounds were analyzed to construct a chemical "sequence" that can be analyzed like a nucleotide sequence, with each compound being analogous to one nucleotide position on the DNA. From this sequence we are able to construct phylogenies that show relatedness of species. All three lines of evidence (morphological, chemical, and DNA) were used to determine final systematic and taxonomic placements of 15 Hydnellum species."

Here's a note about the taxonomy of Hydnellum caeruleum. In 1919 Coker described the species Hydnellum ferrugipes that he considered to be closely related to H. caeruleum. Hydnellum ferrugipes is supposed to lack blue zone lines when fresh and only have blue zone lines after drying. In addition, Coker mentioned that H. caeruleum was only found under pines or conifers, where H. ferrugipies was found under hardwoods. Maas Geesteranus noted that in the true species concept of H. ferrugipes the fruiting bodies lack clamp connections. In our study, the collections examined from both pine and oak forests had blue in the context and had clamp connections. So we conclude that H. ferrugipes is the same species as H. caeruleum. Because H. caeruleum is an older name we use that name instead of H. ferrugipes.
many Hydnellum speciesThere are many other species of Hydnellum, as shown to the right. We think you will agree that there are some strikingly beautiful species. For those of you keeping track (there *will* be a quiz at the end...), the species are a. H. regium, b. H. peckii, c. H. chrysinum, d. H. aurantiacum (teeth), e. H. suaveolens, f. H. cyanopodium, g. H. aurantiacum (top), h. H. mirabile, i. H. ferrugineum (=H. pineticola), j. H. spongiosipes.

Species of Hydnellum can be distinguished based on macromorphology and micromorphology.

Macromorphological characters used to identify species include:

Micromorphological traits used to distinguish species of Hydnellum include, spore size, ornamentation, and the presence or absence of clamp connections.

We hope you enjoyed learning something about Hydnellum species today. They're really quite beautiful and very important as mycorrhizae in forest ecosystems.

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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