Tom Volk's Fungus of the Month for August 2002

This month's fungus is Agaricus augustus, the Prince

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Agaricus augustus, the Prince, from New Mexico

The beautiful Agaricus augustus [uh-GARE-ih-kus uh-GUST-is] is considered by many to be the most delicious of the edible Agaricus species, with a very distinct and strong almond flavor. This mushroom occurs in western North America, west of the Great Plains, and is also relatively common in some parts of northern Europe. It is a happy find for any mushroom hunter, although it is reported to be difficult to find them before the worms do! Like other Agaricus species, the Prince grows on rich organic substrate, often as a litter decomposer in nature. It is probably a secondary decomposer, which means that bacteria and other fungi have to break down raw materials before Agaricus can grow. On a commercial scale this is the process known as composting.

The Prince can have caps about one foot (30 cm) in diameter, although many mycophagists prefer to eat them when unexpanded because of their better texture and odor. As you can see in the picture, the gills turn chocolaty brown when the spores are mature. However, even somewhat expanded caps can show gills that are still white. The beautiful veil and scruffy to shaggy stem (at least when young) are also hallmarks of this species.

Agaricus augustus from California

You may recall from earlier reading of my web pages that another member of this genus, Agaricus bisporus, is the most commonly cultivated mushroom in North America. The blander, "mushroomy" flavor of A. bisporus is certainly far different from the sweet almond flavor of A. augustus. Surprising to most people is that there are several other almond-scented Agaricus species, some of which are rather common in some places. These include the white A. arvensis and A. silvicola, and two species that look very similar to A. augustus, namely A. perrarus (=A. smithii), found among sitka spruce in the pacific Northwest, and A. subrufescens. A. subrufescens is more common east of the Great Plains, usually in the summer, but only when it's very wet. I've only found it a couple of times. It also has a distinct almond odor, but tends to be smaller and more yellow than A. augustus. Interestingly, A. subrufescens was widely cultivated commercially in the early 1900's, but was overtaken in popularity by A. bisporus. No one has been able to explain to me why this happened, but I suppose it has something to do with Amercans' generally bland tastes. (How else could you explain Wonder bread, ketchup, light beer, and prepackaged "American cheese food" slices?) Just think about how our perception of the words "mushroom smell" would have been different if A. subrufescens had won the battle of the agarics!!

Besides the many delicious edible species of Agaricus, there are a number of poisonous species of Agaricus. This includes, but is not limited to, many of the species that stain yellow where bruised or scratched. If you've ever tried to use a key, you know that Agaricus species are notoriously difficult to identify, since the limits of the species have not been well-studied. Some Agaricus species, (such as A. xanthodermus and A. placomyces) are poisonous, causing mild to severe gastrointestinal upset, so you must be *absolutely* sure of your identification, not only to the genus, but also to the species, before eating any wild mushrooms.

Caesar AugustusThe origin of the name Agaricus augustus is, of course, an interesting one. I always have to know the origins of the names of things -- I even teach a course called "Latin and Greek for Scientists." The epithet "augustus" likely derives from the same origin as the month of August-- from Caesar Augustus. Caesar Augustus completed the calendar reforms started by Julius Caesar in 46 BC, and in the process renamed "sextilis mensis" -- the sixth month-- to "Augustus mensis" --Augustus' month-- in 8 BC (yes I know there are conflicting dates reported in various places). He also added one day to his month, stealing it from February as Julius Caesar had done, in order to bring it up to thirty one days, equal to Julius Caesar's Month (July). February was apparently an unpopular month, because it "contained an unpleasant religious observance" (anyone know what that would have been?). See A history of the months and the meanings of their names and How August became so August for more information.

There are two likely associations of this mushroom with Caesar Augustus. The mushroom, with the common name "the Prince," is robust and stately, as was Caesar Augustus, . Maybe in the areas where it was named (Fries named it in Sweden in 1838) it also happened to come out in August. Or it simply may be that this mushroom was very "august," as in "imposing, grand, eminent, dignified, noble, or majestic." Of course that's why Caesar was described as being so "august." You may let your imagination run on this one, since I can't find a definitive answer anywhere. There is no evidence that this mushroom was eaten by Caesar Augustus; he probably preferred Amanita caesarea.

I hope you enjoyed learning something about Agaricus augustus and its relatives today. This mushroom is "august" in many ways!

Thanks to my graduate student Sean Westmoreland for suggesting Agaricus augustus for the August FOTM. If you have recommendations for future FOTM's please write to me at

If you have anything to add, or if you have corrections or comments, please write to me at

This page and other pages are © Copyright 2002 by Thomas J. Volk, University of Wisconsin-La Crosse.

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