#185: Stropharioid Mushrooms

The stropharioid mushrooms include agarics from the genera Stropharia, Hypholoma, Psilocybe,* and Pholiota. Mushrooms in this group produce a brown to dark brown spore print, have attached gills, and form a partial veil. There are actually quite a few mushrooms that can fit this description, so you might have to check some microscopic features to be sure your mushroom belongs to this group. Stropharioid mushrooms should have a cap surface composed of thread-like cells and have smooth spores with distinctive germ pores.¹

Description

Stropharioid mushrooms have relatively few features that are shared by all species in the group. The unifying macroscopic characteristics are: a brown spore print, attached gills, and a partial veil. This sounds reasonable in theory, but it’s a bit tricky in practice. Spore print color is variable and ranges from light brown to dark purple-brown. Sometimes it is difficult to decide whether gills are attached or free. On top of that, the partial veil is sometimes very ephemeral and may not leave any trace. Luckily, stropharioid mushrooms often grow in dense clusters, which makes it easier to find mushrooms in multiple stages of development. This is a huge help when checking for the presence of a partial veil and even when assessing gill attachment. Stropharioid mushrooms are all saprobic but decompose a variety of substrates, from wood to grassy debris to dung.^1,2

With so few visible features tying the group together, it is important to discuss the microscopic characteristics of the stropharioid mushrooms. The two most important features to check are: the shape of the cells on top of the pileus and the texture of the spores. Stropharioid mushrooms have pilei composed of filamentous cells. In other words, the top of the pileus should look like a tangle of fibers when viewed through a microscope. This easily separates the mushrooms from ones with a cellular pileus surface, which would be composed of large and inflated or block-like cells. Stropharioid mushrooms produce spores that are smooth and have a noticeable germ pore. The germ pore looks like a small gap in the spore’s wall and is usually found at one end of the spore. These features can help distinguish the stropharioid mushrooms from similar species. For example, the genus Gymnopilus (which is not quite stropharioid) produces spores with a bumpy coat. One final microscopic feature that stropharioid mushrooms share is parallel lamellar hyphae. If you look at the cross-section of a gill (a.k.a. ‘lamella’), the hyphae in the center are more or less straight and all travel up and down.¹

Among the stropharioid mushrooms, the easiest genus to pick out is Pholiota. Unlike the other stropharioid mushrooms, Pholiota produces light brown spores that are anywhere from yellow-brown to reddish-brown. Pholiota species always grow on wood (though the wood may be buried) and usually retain small pieces of the partial veil around the stipe as a ring and on the edge of the pileus. The spores from these mushrooms often have very small germ pores that can be difficult to see. 2–4

The most commonly encountered Hypholoma mushrooms usually appear on wood. They produce purplish-brown spores and lack partial veil remnants, which easily separates the genus from Pholiota. Other species of Hypholoma grow in boggy or mossy areas. These tend to be small and often fruit singly, which makes identification difficult. The combination of a purple-brown spore print, the presence of a veil but lack of remains, the smooth spores with germ pores, and a filamentous pileus surface will eventually lead you to this genus.^2,5

Stropharia species usually are medium-sized to large mushrooms, have a thick fleshy texture, produce persistent rings, and deposit purple-brown spore prints. These mushrooms decompose a variety of debris on the ground, including: grass debris, humus, wood, and dung. Although they can decompose wood, Stropharia mushrooms rarely fruit directly from the wood. The main exception to this is when the wood is in the form of woodchips.^1,2,6

Species of Psilocybe are very similar in appearance to Stropharia, but tend to be smaller, have thinner flesh, and have fainter partial veil remnants. Most Psilocybe species produce a ring zone – a thin area on the stipe where the partial veil connected that becomes visible as falling spores get stuck in it – rather than proper rings. The dark purple-brown spores make the ring zone easily visible. Some species of Psilocybe stain blue, which is something that never happens in Stropharia. Psilocybe mushrooms also appear in similar habitats to Stropharia, but have more of a preference for rich soils. They commonly fruit in dung, humus, woodchips, and gardens. The morphological characteristics that separate Psilocybe and Stropharia are not very consistent, so species are frequently swapped between the two genera. As a result, field guides may be inconsistent on which species belong to which genus.^2,6

Similar Species

Agaricus (FFF#174) species, non-deliquescent coprinoid mushrooms (FFF#177), Bolbitaceae species, and cortinarioid mushrooms can all appear similar to stropharioid mushrooms. The most reliable way to separate these mushrooms is by checking microscopic characteristics. Alternatively, you can go out and identify as many mushrooms as possible to get a feel for what the genera should look like. Our brains are good at categorizing things, so the more you see stropharioid mushrooms the easier it will become to identify them without consulting microscopic features. Exactly how this works is impossible to put into words; it is more of an intuition than a logical assessment of features.

To some extent, I don’t think it is important to know the differences between stropharioid mushrooms and similar species. I can tell the difference between Stropharia and Cortinarius, but I will always have to consult a key for something with an intermediate morphology. Of course, different field guides sometimes deal with those interstitial mushrooms differently. Getting to know how your field guide works is perhaps more important than remember the differences between morphological groups.

Edibility

There are very few edible stropharioid mushrooms. The best edible in the group is Stropharia rugosoannulata (FFF#193), known as the Wine Cap or King Stropharia, and is actually cultivated in Europe. Hypholoma sublateritium (FFF#125), the Brick Cap, is sometimes considered edible and other times labeled poisonous, but is probably the best-known “edible” from Hypholoma. Pholiota has even fewer edible species, since most mushrooms in that genus cause gastrointestinal distress (FFF#099). The most interesting stropharioid mushrooms belong to the genus Psilocybe. Many Psilocybe mushrooms contain the hallucinogenic toxin psilocybin (FFF#098), which some people use as a recreational drug.^2,3

Taxonomy

Traditionally, stropharioid mushrooms were placed in the family Strophariaceae and divided among four genera: Stropharia, Hypholoma, Psilocybe, and Pholiota. However, mycologists cannot agree on which mushrooms should fall into which genus. Consequently, these mushrooms often get shuffled around. So far, DNA has not improved the picture. Even with genetic analysis, the lines between the genera are unclear. Mycologists now seem to be debating whether to solve this problem by making the genera less specific (for example, by combining all four genera into a very large Psilocybe) or more specific (thereby requiring additional genera, such as Leratiomyces).^5–7 This debate will probably remain unsettled for decades, so get used to frequent name changes.

The most significant finding from DNA analysis of stropharioid mushrooms is that Psilocybe actually contains two separate lineages of mushrooms: one containing the mushrooms with psychoactive toxins and the other containing the mushrooms without them. The non-psychoactive lineage is monophyletic with Stropharia, Hypholoma, and Pholiota, while the psychoactive lineage (which is also the blue-staining lineage) is not. To resolve this, the psychoactive lineage kept the name Psilocybe but was transferred to the family Hymenogastraceae. The other group remained in the Strophariaceae but was renamed Deconica.^7–9 Other members of the hymenogastraceae include false truffles⁸ and the agaric genera Galerina,¹⁰ Gymnopilus,¹¹ and Hebeloma.¹² The agaric mushrooms in this group may key out with either the stropharioid mushrooms or the cortinarioid mushrooms in your field guide. Most field guides have not yet caught up to taxonomy, so I did not separate Psilocybe and Deconica in the “Description” section of this post. [NOTE]

Another contribution from DNA is that the genus Agrocybe now belongs to the Strophariaceae.¹³ However, this was a recent change and Agrocybe probably keys out with the cortinarioid mushrooms or the Bolbitaceae in your field guide.

Kingdom	Fungi
Division	Basidiomycota
Subdivision	Agaricomycotina
Class	Agaricomycetes
Subclass	Agaricomycetidae
Order	Agaricales
Family	Strophariaceae Singer & A.H. Sm.14 Hymenogastraceae Vittad.15