Tom Volk's Fungus of the Month for September 2003

This month's fungus is Gastrocybe lateritia, the bean sprout fungus.

--by Heather Hallen and Tom Volk

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Heather Hallen, Hello my name is Amanita virosaThis month's fungus is the favorite of this month's coauthor, Heather Hallen of Michigan State University. I have known Heather for many years, collecting mushrooms with her and listening to her speak eloquently at many mushroom forays and mycology meetings. Heather has completed her PhD thesis on Amanita toxins, especially amatoxins, but one of her side projects was this interesting little bean sprout fungus. Heather became interested in this fungus because it is a relative of Conocybe filaris, another mushroom that contains amatoxins.

Gastrocybe lateritia

As you can see, Gastrocybe lateritia looks more like a slimy, sickly bean sprout than a mushroom, hence the common name. Actually, this fungus lacks a "real" common name - maybe too few people pay it attention for it to merit that honor - but Heather has been calling it by that name for years, and maybe it will catch on. You can read more about common names for mushrooms by visiting, where you may vote on which common names you like best.

If you live in the eastern midwestern United States or Canada, and are up and about in the morning, you might come across Gastrocybe lateritia. This fungus is locally common on lawns in the Great Lakes region between June and September. Heather became interested in G. lateritia when she noticed it fruiting each morning on the lawn in front of Plant and Soil Sciences at Michigan State University, amidst the Conocybe lactea specimens she was studying.

G. lateritia is one of the common mushrooms that are found in rich, usually unpesticided and unherbicided lawns. If you are patient in studying this mushroom's development, you can observe that the immature button of this mushroom emerges around 8:00 in the evening. Overnight the mushroom expands. The basidiospores mature between 7 and 10 the following morning, and, by 10:30 or so, the fungus has dried up, effectively vanishing. The long, hollow stem often cannot bear the weight of the watery, slimy cap, and the whole thing usually topples over. Unlike most mushrooms, the basidiospores cannot be forcibly discharged-- due to the slime and the partial autodigestion of the gills-- and thus have to wait for the cap to weather or rot away to be released. Why on earth would this happen? And how could this seemingly inefficient species survive evolutionary pressures? As it turns out, G. lateritia it not alone in this dilemma.

G. lateritia has been considered a sequestrate (or secotioid) basidiomycete, that is, a mushroom that has lost the ability to forcibly discharge basidiospores and may be on its way to developing a subterranean truffle-like form. Gills or pores may still be recognizable in some species, but these remain enclosed until the fruiting body weathers away or is eaten by animals. Sequestrate fungi have evolved separately in many different lineages. Some examples are Thaxterogaster (sequestrate Cortinarius), Longula (sequestrate Agaricus), Gastroboletus (sequestrate Boletus), Torrendia (sequestrate Amanita), Montagnea (sequestrate Coprinus), Macowanites (sequestrate Russula)... the list goes on.

Sequestrate fungi are primarily found in arid regions, which do not favor more "ordinary" mushrooms. The peculiar malformed-mushroom morphology is thought to be an ill-adapted bottleneck through which a fungus passes en route evolutionarily to going underground as a truffle. Both sequestrates and truffles have the potential advantage over mushrooms in that they are able to protect their gills and spores from drying out before the spores are ready. In addition, many of them emit delightful odors, and thus attract mammals and insects, which eat the fungi and inadvertently disperse the spore in their feces. Thus the spores are deposited some distance away, conveniently pre-packaged with a bit of nutritional feces to get them started.

So where does this leave Gastrocybe, favoring decidedly non-arid locales such as Michigan and Wisconsin lawns? The slimy cap of Gastrocybe is also mysterious, as sequestrates are, by and large, dry.

Conocybe jumbleIn 1969, Roy Watling recognized that there were several similarities between Gastrocybe lateritia, which he described from a Michigan herbarium specimen, and fungi in the family Bolbitiaceae, notable Conocybe and Bolbitius. Although Bolbitius can have a slimy cap, it does not topple over under its own weight, and it also has forcible spore discharge. More strikingly similar are Conocybe species, which share many ecological features with Gastrocybe. Both fungi have the same fruiting season, emerge as buttons at the same time in the evening, undergo spore maturation at the same time in the morning, and wither and disappear by 10:30 AM. All three genera have microscopic similarities, including the size and shape of the spores, as well as the structure of the gills, when present. The sequestrate form inspired him to give Gastrocybe lateritia its own, new genus, but with the understanding that it was closely related to these other fungi.

Interestingly, intermediate forms exist between C. lactea and G. lateritia, in which the cap is white (like C. lactea) but collapsed and with deliquescent gills (like G. lateritia), or brown and viscid (like G. lateritia) but open (like C. lactea). The photo above and to the left shows a mixture of Gastrocybes (slimy red-brown), intermediates (slimy white; viscid expanded caps), and C. lactea (whiteish, non-viscid expanded caps).DNA sequencing revealed that Conocybe lactea and Gastrocybe lateritia were sister species - each was the other's closest relative. Some of the intermediates grouped with C. lactea and others with G. lateritia; the morphology of the intermediate made no difference. Perhaps most interesting, every time Heather tried to culture G. lateritia, she obtained an odd bacterium (in the Chryseobacterium gleum/ C. indologenes group, a gram-negative Flavobacterium) that was resistant to high levels of antibiotics and thus could not be eliminated from the culture. The working theory is that Gastrocybe lateritia looks sick because it is, in fact, sick; it is a Conocybe with a bacterial infection.

Conocybe lacteaThere are many small lawn mushrooms in addition to Gastrocybe. To the right is a beautiful Conocybe lactea, but there are many more. Most of the poison calls that come in to Poison centers are from babies "grazing" in the lawn. The distraught mother calls the poison center and I get a phone call. Fortunately most of these are very benign, since poisonous mushrooms are not common in lawns. However they do exist in some places.

Gastrocybe and lawn Conocybes are not known to contain any toxins, unlike another common lawn mushroom, Panaeolus foenisecii (=Panaeolina foenisecii , =Psilocybe foenesecii) that is known to contain very, very small amounts of a hallucinogenic compound. In some areas of the world there are deadly lawn mushrooms, so don't assume you can eat a mushroom just because it's common. Especially never eat mushrooms from heavily pesticided and herbicided places, such as the neighbor's lawn or a golf course.

We hope you've enjoyed reading about Gastrocybe lateritia, and that it might inspire you to take a closer look at this fascinating fungus if you're lucky enough to have it on your lawn. You can read more about Gastrocybe in this paper: Hallen HE, R Watling & GC Adams. 2003. Taxonomy and toxicity of Conocybe lactea and related species. Mycological Research 107(8): 969-979

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