Tom Volk's Fungus of the Month for March 2002

This month's fungus is Amanita caesarea, Caesar's mushroom.

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Amanita caesarea or something like that

Beware the Ides of March.

Besides being interesting for its edibility and controversial taxonomy, this month's fungus has lots of history behind it. Amanita caesarea and its American relatives Amanita hemibapha and Amanita jacksonii are among the relatively few widely-consumed edible Amanita species. The genus Amanita is better known for its poisonous members the death angels (Amanita virosa, A. bisporigera, A. verna), the destroying angel or death cap (A. phalloides) and the hallucinogenic and toxic fly agaric (A. muscaria). There are many hundreds of species of Amanita across all the continents (except Antarctica), including dozens if not hundreds of species that are still unknown to science, waiting to be discovered. The species of Amanita are fairly narrowly defined, and we have little information about the edibility of most species. Because of the possibility of poisoning combined with the difficulty of identifying the species correctly, you should be very careful about eating any Amanita specimen. Amanita is definitely not recommended for mycological beginners. Every year many people are poisoned, thinking they are eating an edible species when they are in fact eating a deadly Amanita.

Amanita parts labeled Amanita is a well-defined genus of mycorrhizal Agaricales (gill forming mushrooms) that have a white spore print, gills (lamellae) that are free from the stipe (stalk) and a universal veil covering the young mushroom buttons. When the mushroom expands, the universal veil is broken; the bottom of the universal veil forms the cup shaped volva at the base of the mature mushroom. The top of the universal veil is often left at the top of the mushroom cap, forming a patch or sometimes breaking up into scaly floccules. Most species also have a partial veil, a membranous structure that protects the developing gills of the young mushroom. When the mushroom cap expands, the partial veil breaks and is left as a ring (annulus) on the stalk. See the picture to the right for labeling of these various parts of the mature mushrooms and the expanding button. Some Amanita species, such as A. fulva and A. vaginata lack the partial veil and annulus. Almost all other genera of mushrooms lack the universal veil and volva-- a notable exception is Volvariella, but that genus has a pink spore print and always grows on wood or other debris, including other mushrooms.

The harbor at Caesarea, a remnant of the Crusades in IsraelAs you might guess from the name, Amanita caesarea was a favorite of the emperors of the Roman Empire, the Caesars. Perhaps Julius Caesar ate a meal of this delicious mushroom before Brutus did him in on the Ides of March (March 15). Et tu Brute?

However, the most famous killing involving Amanita took place in ancient Rome circa 50-60 A.D. The Emperor Claudius had ascended to the throne after the assassination of his nephew Caligula. We've all heard about the decadence (and Roman porno movies, such as "Veni, Vidi, Veni") associated with Caligula. Anyway, Claudius had several wives, but finally married his fourth wife Agrippina, who was also his niece. Agrippina already had a son from a previous marriage, Nero, for whom she had great plans. She persuaded Claudius to adopt Nero, putting him in line for the throne, should something happen to Claudius. (You can see where this is going already.) Agrippina was an impatient woman, and could not wait for a natural death for Claudius; she plotted to kill him by feeding Claudius his favorite meal, Amanita caesarea, laced with extracts from Amanita phalloides, the death cap. When the symptoms set in the next day, a co-conspirator doctor Xenophon administered an enema of colocynth, a potent toxin from a plant called bitter apple, which together with the mushroom toxin killed Claudius. Nero and his fiddle thus became emperor, and the rest, as they say, is history.

Amanita buttons in Texas It is pretty well accepted that true Amanita caesarea does not exist in North America, having been described from the Italian region. So although Amanita caesarea is the fungus of the month, none of the picture on this page are really Amanita caesarea. To the right is (probably) Amanita hemibapha from Texas; the pictures above, from Connecticut, are likely Amanita jacksonii. These two species are collective called the "American Caesar's Mushroom." As currently circumscribed, Amanita species are very narrowly defined, and species identification is difficult, at best. There are significant microscopic differences between the three species, and until someone does the molecular (DNA) studies on this group, we should consider them to be different species.

The picture to the right also illustrates why you should carefully dig under mushrooms when you are collecting them. If you just pulled these mushrooms out by their stems you might miss the diagnostic character, the volva. Looking back at the pictures on this page, I should also point out that these mushrooms are *much* more beautiful when you see live fresh specimens. There are also much better, very beautiful pictures of these mushrooms in existence, but I do not see this mushroom very often-- never in Wisconsin.

I hope you enjoyed learning something about Amanita caesarea and its relatives today. There's lots of history behind some of our most beautiful mushrooms.

Thanks to Dr. Debby Hanmer, plant pathologist in my department, for giving me the idea to have Caesar's mushroom commemorating the Ides of March. Anyone else have an idea for a future FOTM?

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

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