Tom Volk's Fungus of the Month for July 2004

American flagSuillus americanus, the chicken-fat mushroom.         

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Suillus americanus This month's fungus, Suillus americanus, is called the chicken-fat mushroom because of its yellow color (more yellow than the picture at the left) and soft consistency and slippery texture. It's edible, but not considered to be choice by anyone I know. The flavor is ok, but it's really very slimy, as you might guess from all the pine needles stuck to the mushrooms in this picture. Maybe you can pretend it's escargot! It's actually very similar, depending on how you cook it. I've sautéed it in a stir-fry with lots of garlic and managed to get it to be delicious, but your mileage may vary. Interestingly, although it is edible for most people, there are a significant number of people who develop a contact dermatitis (rash) from touching this fresh mushroom. I am not one of those people, but I have noticed that my fingers become very slippery after I have picked several of these mushrooms; it feels as if my fingerprints have rubbed off! Thus, this is one of those mushrooms where you have to worry about such idiosyncratic reactions. Whatever the chemical responsible, it seems to be degraded upon cooking, since even those who get a rash from touching it seem to be able to eat the cooked mushrooms.

Suillus americanus also has an interesting ecological niche, being found in nature growing in association with only one kind of tree, namely eastern white pine (Pinus strobus). So, if I'm walking through the woods with my head to the ground looking for mushrooms and find S. americanus, I know that there is a white pine nearby. For some people, like me, it's the easiest way to identify white pine! For most people, white pine is easier to identify by counting the needles in a bundle: in white pine there are five. This easy to remember because W-H-I-T-E has five letters. In any case, although white pine can be host to many different fungi, Suillus americanus forms mycorrhizae only with eastern white pine-- not even with western white pine or sugar pine, which are closely related. However, despite their intimate association with certain tree species, S. americanus and other Suillus species do not seem to be as ecologically dependent on the tree for their nutrition as other genera of boletes, since they can be more easily cultured in the lab. Unfortunately for potential cultivators, they do not seem to be as delicious as their bolete relatives either.

Suillus americanus, photo by Hal BurdsallBoletes are a group of mostly mycorrhizal, mushroom shaped fungi, distinguished by their pores. Like gills, these pores are lined with basidia that produce basidiospores, serving to increase the surface area. Some of the most delicious and sought after edible mushrooms are boletes, including Boletus edulis and its relatives, the much under-rated Boletus subglabripes and Boletus bicolor, Leccinum species, and Gyroporus cyanescens. In most areas there is a distinctive "bolete season." In the midwestern US they usually prefer warmer weather, beginning to fruit in earnest in mid July and continuing to mid September. In other areas, such as the mountainous west, many boletes begin fruiting in the spring, sometimes just as the morel season is ending.

Suillus cavipes radiating poresThe genus name Suillus roughly translates as "pig mushrooms" probably referring to swine and their soft squishy nature. Members of this genus of boletes are easily characterized macroscopically by the pores, which radiate and elongate out from the stipe to the edge of the pileus. This condition is called "boletinoid" and is shown more dramatically to the left in Suillus cavipes. It is in the genus Suillus that you can most easily see the evolutionary relationship between gills and pores, since these pores are arranged as if they were gills at one time. In fact, until recently, mycologists included the boletes with the gilled fungi in the Agaricales. However there are significant differences between boletes and gilled fungi, so boletes and relatives are placed in their own order, the Boletales.

In general, Suillus species tend to be softer and more "squishy" that their Boletus relatives, and there tends to be more ornamentation on the surface of the cap. Many of the other characters of Suillus are variable and serve to identify species. For example some have viscid caps, while others do not. Some have glandular dots on the stipe. Some have a partial veil that forms an annulus. One microscopic character that holds the genus together is the presence of cystidia on the hymenium that turn orange-brown when 3% KOH is added. Even without a microscope, these cystidial clusters can be seen with a hand lens near the mouths of the tubes. No Suillus species are known to be poisonous. However, some people have experienced gastrointestinal upset upon consumption of the slime layer. In addition, a small percentage of people develop a contact dermatitis on handling some of the species, as mentioned above, especially S. americanus and S. granulatus.

As you probably know from reading my other pages, boletes are not the only fungi with pores. The boletes can be distinguished from the other group of pored fungi, the polypores, in several ways, as shown in this table.




Pore layer

Peels off

Does not peel off


Mycorrhizal, i.e. with a mutualistic association with roots of trees

Wood decay

Fruiting location

Typically on the ground, fruiting from the roots of trees

Typically directly on wood, although may be on the ground from buried wood.


Typically mushroom shaped

Typically in the form of a shelf or some other shape

So you can see it's usually easy to distinguish between boletes and polypores, although there are a few that will give you trouble by breaking the rules. For example, members of the genus Albatrellus are considered to be polypores because their pores don't peel, even though they are mycorrhizal. Polyporus radicatus and several related polypores without peeling pores almost always grow on the ground, but if you dig down, you can almost always find the piece of buried wood from which the fungus is fruiting. There are also a few boletes, like Boletus mirabilis that climb up on logs to fruit, raising themselves up to get their spores further into the air stream. In fact some mycologists argue that some of these boletes may not be mycorrhizal after all. Fortunately, most boletes and polypores follow the rules.

chicken-- aaaggggh!Since I chose the chicken fat mushroom for Fungus of the Month, I could not ignore the famous song "Go you chicken fat, go." In the early 1960's, President John F. Kennedy, as part of his Youth Fitness program, commissioned this song from Meredith Wilson, whose "Music Man" was all the rage at the time. Robert Preston, who starred as Professor Harold Hill in "The Music Man," sang the six and a half minute song, and the record was distributed to every school in the United States. (For you youngun's, a "record" is a large vinyl circular disc that was played on a record player or turntable by placing a needle that was moved along the single spiral groove as the record was rotated). The intention was that the "Chicken Fat" song would be played on the loudspeaker every morning as students did their calisthenics. If you click below you can hear the first minute or so (~2..5 megabytes) of the song. For the full 6.5 minute version click here (.MP3 file- scroll down the page) or here (.MOV file-- starts playing automatically). How could you not love a song with such inspiring lyrics as "Give that chicken fat back to the chicken, and don't be chicken again...?" However, don't blame me if the song gets stuck in your head, and you can't get it out! Thanks to my graduate student, Adam Gusse, who grew up in the 1980's hating this song (and his sadistic gym teacher), but still suggested the song for inclusion here.

I hope you enjoyed learning something about Suillus americanus and friends. You should be able to start finding it in the woods, wherever eastern white pine is found. You don't have to eat it, but maybe you can give your chicken fat mushroom back to the chicken? Happy hunting!

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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