Continuing on the theme of long overdue posts (referring to my previous post discussing hemlock reishi, Ganoderma tsugae), my surprise encounter in late May of 2016 with an extensive patch of Agaricus bitorquis was probably one of the most fruitful foraging adventures of that whole year. I was nearly in hysterics after discovering these hefty beasts discretely heaving themselves up and through mounds of wood chips. I couldn’t keep it together for quite a while thereafter, as I still have a problem with getting way too excited about these sorts of things.
Agaricus bitorquis, also known as the ‘spring agaricus’ or ‘pavement mushroom’ (I’ll get into that in a bit) is a large, distinctive mushroom in the Agaricus genus which includes the common white button, cremini and portobello mushroom (which are all just different varieties of the same species, A. bisporus) as well as some of the more well known wild species such as meadow (A. campestris) and horse mushrooms (A. arvensis) that like the spring agaricus are all choice, delicious edible mushrooms.
If you would like to know more about the meadow and horse mushrooms or other species within the Agaricus genus in general, then I recommend you check out my two previous posts on the subject, Foraging Fun: Agaricus and Foraging Fun: Agaricus campestris. I also cover most of the basic identification features for the genus as a whole in the articles as well as some other fungi that resemble them that you definitely wouldn’t want to confuse them with including the notoriously deadly Amanita verna & A. phalloides.
Now that you’re up to speed on the details, that is if you weren’t already, then let’s continue on about A. bitorquis. This mushroom is called the ‘spring agaricus’ because it often fruits earlier than the other two latter species that I have mentioned here, which you can expect to find from about mid June at the earliest to late October or early November at the latest. I found this particular ensemble or specimens fruiting on May 23rd of 2016, which is a lot earlier than I would have expected to see mushrooms this large making a break for it.
A. bitorquis is a widely adaptable species, favoring heavily disturbed environments rich in partially decomposed, nitrogenous material. I discovered these mushrooms growing along the curb by a street leading into a park out of a thick layer of wood chips that had been spread under a grove of Norway spruce (Picea abies) trees. It is not uncommon to find A. bitorquis fruiting from in between patio or sidewalk stones, beside boulevards or trails, along the sandy or grassy shoulders of roads and other well traveled areas in urban or suburban environments close to human activity.
It also certainly isn’t unheard of to see this species force it’s way through or around the cracks in pavement, hence the name ‘pavement mushroom’. This is a true testament to the strength, durability and resiliency of fungi, to be able to generate enough force continuously in order to break apart asphalt. A quick Google search will reveal half a dozen or so, if not more, photos showing the sorts of places that these extraordinarily mushrooms find themselves. Here are just a few to wet your whistle:   .
Other than habitat, A. bitorquis is quite similar in a lot of ways to the horse mushroom (A. arvensis) however the latter is more likely to be found growing along the edge of a field or in a rich, grassy meadow rather than beside a parking lot. A. bitorquis is generally a large, stocky mushroom with a fairly dense, dry, fleshy cap that can be between 4 or 5″ all the way to even 8 or 10″ across and is often white to buff colored, occasionally with scales present, and more or less flat, sometimes with a wavy margin when mature. The stem is also quite thick and fibrous, bulbous at the base and retains a distinct ring or annulus that encloses the gills under the expanding cap when young.
The gills are quite numerous, crowded, free from the stalk (only attached to the cap) and quite a lovely pink color when young, maturing to a deep chocolate brown after going through pale lilac and light brown phases. The spores are also dark brown or almost black. Neither the cap nor the stalk or bulbous base of the fruiting body stains yellow after being bruised or cut, which is typical of both the horse mushroom, which slowly stains only a light yellow, and the yellow straining agaricus (Agaricus xanthoderma), a mildly poisonous* species, that quickly stains a bright, almost neon yellow after only seconds of exposure to the air.
Agaricus bitorquis can be found fruiting alone but is more frequently found in groups or even fairy rings where there is enough room for the mycelium to expand and adequate nutrients. Usually the caps will only partially emerge from or be level with the ground where they are growing, leaving tufts of grass or piles soil, gravel, chunks of asphalt or other debris shoved aside as the often massive caps push their way through the substrate. This makes it difficult to assess the specimens for some of the other necessary identification features without handling them.
Once you have confidently identified your spring agaricus mushrooms, you will likely have to clean the debris from the cap, which is best performed with a stiff brush in the field so as not to bring some of the habitat back home with you. Younger specimens are usually best, as they are less likely to contain insect eggs, fly larvae, or be mushy and waterlogged from absorbing excess moisture or rainfall. However, large, young mushrooms (as I was lucky enough to find) of excellent quality are relatively common with this species.
Disclosure: Since this is an Agaricus that enjoys growing in close to or seemingly in direct association with human disturbance, it isn’t wise to harvest these mushrooms if they are growing in what is likely to be an environment polluted by trash, road salt, car exhaust and other contaminates which could obviously be unhealthy. The specimens I found were growing in a park, although in retrospect were still quite close to the road, but ultimately this is a decision that you as an individual have to make. Even though this is common sense I felt the need to mention it, just in case, because we can all get a bit too eager sometimes.
*Agaricus xanthoderma is known to cause anywhere from mild to severe gastrointestinal distress (we all know what that means) after consumption but is not deadly poisonous, so you’ll live but it won’t be fun. There are a few rare individuals that report consuming this species with no ill-effects, however there’s enough evidence to suggest that it’s best to leave this species alone. Definitely take the time to learn how to differentiate the yellow stainer as well as the Amanitas when foraging for edible Agaricus mushrooms.