Entoloma abortivum, the Aborting Entoloma, a.k.a. Hunter's Heart, Totlcoxcatl, or "ground prunes"

Tom Volk's Fungus of the Month for September 2006

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My former student, Bernadette O'Reilly, is now at Duke University getting her Ph.D., and she needs your help in geting samples of Entoloma abortivum from as many locations as possible. Click here for a pdf file (321 kb) that will give you all the details about how you can help the progress of science.

This month's fungus is actually two fungi for the price of one-- no extra charge! It's the fifth anniversary of our publication on this unusual relationship. The most common common name for the fungus is the "aborted Entoloma." We'll see later why this name is incorrect. This fungus is sometimes called "hunter's heart," which I've never quite understood. Is it the heart of a hunter rotting in the forest? Very confusing. In some parts of Mexico these fungi are sold in the market as Totlcoxcatl. Anyone know what that means? Click here for the answer. My favorite name for this fungus is the "ground prune," which very aptly describes the shape and location of the lumpy forms.

Entoloma abortivum is a forest-inhabiting gilled mushroom that has been reported to be found in two forms: a typical mushroom fruiting body with a gray stipe, a gray cap, and pink, short-decurrent to adnate gills (A in the picture to the left), and a white carpophoroid ("aborted") form lacking well formed gills (B in the picture to the left). There's also another mushroom involved-- Armillaria gallica, one of the honey mushrooms (C in the picture to the left). So what's going on here? The three forms of the fruiting bodies are often found together in one area, but can also be found with two of the forms (normal Entoloma + carpophoroids, normal Armillaria + carpophoroid and normal Entoloma with normal Armillaria) or sometimes with just one species fruiting. Armillaria gallica is most often found alone.

So, what are these "carpophoroid" things?

Prior to 1974, carpophoroids were believed to be E. abortivum fruiting bodies that never developed properly. They were described as "the gastroid or atavistic aberration of an otherwise gymnocarpic fungus." Roy Watling was the first to publish a paper in 1974, changing this interpretation by reporting that the carpophoroid form of E. abortivum is not comprised solely of E. abortivum hyphae. Through his studies of cultures prepared from agaricoid and carpophoroid forms of E. abortivum, Watling (1974) concluded that there was a second fungus present in the carpophoroids that was absent in the agaricoid fruiting bodies. This second fungus usually sectored out in culture and produced a darker mycelium with black rhizomorphs. Through an analysis of these rhizomorphs, the luminosity of his cultures, and the results of hyphal fusion experiments, Watling (1974) identified the second fungus as Armillaria mellea in the broad sense. [I have since learned that Nancy Weber and Sam Ristich had separately earlier showed that both Entoloma and Armillaria were involved, but these observations were not published] Since Armillaria at that time was considered to be a pathogen with a very wide host range, Watling naturally postulated that Armillaria is the parasite of Entoloma abortivum. This view was widely accepted and became incorporated into mushroom field guides.

However, over the years, I (and others) had made some observations that called this interpretation into doubt. First the carpophoroids *taste* like Armillaria, with that metallic taste typical of Armillaria gallica. We had noticed half-aborted fruiting bodies of Armillaria-- in clusters. We could find some mostly aborted fruiting bodies with an annulus on the stalk-- characteristic of Armillaria, not Entoloma. We found carpophoroids attached to the black rhizomorphs, exactly in the spot where Armillaria fruiting bodies would be expected to be found. The flesh of the mushroom had a tendency to bruise pink, a characteristic of Armillaria. We even found a completely aborted cluster with many stems inside.

FIGS. 2-8. Detail and variation of carpophoroids of Armillaria/Entoloma. 2. Section of a carpophoroid showing outermost layer of tissue (A), area ("the rind") that represents malformed gill tissue (B), and the inner matrix (C). 3. Cluster of carpophoroids arising from a rhizomorph. Although most mushrooms in the cluster developed into carpophoroids, the 4 mushrooms on the right are agaricoid Armillaria gallica. 4. Armillaria fruiting bodies with carpophoroid caps, but stipes that are morphologically unaffected. 5. A continuum can sometimes be seen from fully developed carpophoroids (on the left), to fruiting bodies with carpophoroid caps or no cap and Armillaria stipes (on the right), to agaricoid Armillaria with fully developed caps (not visible in this photo). 6. Rhizomorphs attached to base of carpophoroid. 7. A massive cluster of carpophoroids comprised of many malformed mushrooms (the cluster on the left is approximately 25cm long). The stipes of all the mushrooms originate from a common point, usually a group of rhizomorphs. This type of fruiting is typical of Armillaria spp. 8. Carpophoroids sometimes produce a rudimentary partial veil. Scale bars in Figs. 2-8 = 1 cm.

Dan Lindner (Czederpiltz), an undergraduate at UW-Madison at the time, came to work on this problem with me and Hal Burdsall at the Forest Products Lab in Madison. Dan had made similar observations, and we decided to try to duplicate the relationship in the lab to study what happens. Dan did several interesting cultural experiments that are described in our publication, and he was able to "abort" Armillaria tabescens fruiting bodies in Petri dishes. We also looked at hyphal actions under the microscope, but these were inconclusive. Later, another undergraduate in my lab, Bernadette O'Reilly, showed that the hyphal interactions between the two species were complex and unpredictable. We had expected to see the hyphae intertwining or repelling one another, but they seemed to pass one another without significant interaction. There were many technical difficulties, and we will repeat these experiments sometimes using other staining and cultural methods.

However, after reading our publication it seems very likely from our work that Entoloma is the pathogen, not Armillaria. We have not ruled out the possibility that the parasitism goes the other way, or that the nature of the relationship is something other than parasitism, but we have no evidence of either of those scenarios. I'll let you read our publication, and you can decide for yourself.

So according to our data, the field guides are mistaken on this point-- Entoloma should be considered a pathogen of Armillaria. We recommend the name "Aborting Entoloma" for the common name. Moreover, the carpophoroids should be referred to as Aborted Armillarias.

***The Mexican name for the carpophoroid (aborted Armillaria) is Totlcoxcatl, which means "turkey wattle." Isn't that a cool name?