Agaricus bitorquis, commonly known as The Pavement Mushroom or The Banded Agaricus, is an edible species of mushroom found in the Northern hemisphere. It thrives in urban environments, specifically within roads, park pathways, ditches, and even manages to emerge through asphalt and gaps between paving slabs.[i]
This mushroom displays several distinctive features, including a stout, compact stem, a dirty appearing cap, and a notable peronate veil that encloses the stem resembling a stocking and forming a double band. The mushroom also does not characteristically change color when bruised or damaged.
This species was first described in 1883/1884 by the French naturalist and mycologist Lucien Quélet as Psalliota bitorquis. However, in 1887 the species was moved to its present genus Agaricus by the Italian mycologist Pier Andrea Saccardo.
The etymology of this species’ name is interesting as it nods to its morphology. The epithet “bitorquis” is a latin-derived term meaning “two-collared” or “with two collars”, referring to the presence of a characteristic double ring on its stem. This double ring forms when the peronate veil, which covers the young gills, separates from the rim of the cap. As a result, thin white annuli appear at two distinct regions of the stem: one higher up and another lower down, where the veil was originally attached.
Lastly, this species has sever synonymous names in various mycological resources and field guides. As such, readers may come across this species under the following names:
- Chitonia pecquinii
- Agaricus campestris var. edulis
- Agaricus rodmanii
- Psalliota bitorquis
- Psalliota peronata
- Psalliota rodmanii
- Psalliota edulis
- Psalliota edulis var. valida
- Agaricus bitorquis var. validus
Cap: The cap of Agaricus bitorquis ranges from 4 to 18 cm in diameter, initially broad and convex, eventually becoming plane or developing a slight central depression. The surface of the cap typically is smooth but in dry weather it may become cracked and become scaly. While the overall color of the cap is white to whitish and it does not change color when bruised, it may discolor sordid yellowish to tan to pinkish in old age or wet conditions. When young, the margin is inrolled and often extends beyond the gills. In some instances, these mushrooms may mature underground or have only a small part of the cap rim visible from above ground, causing the cap surface to be discolored by earth. As such field guides often describe the A. bitorquis’ cap as “dirty white”.
Flesh: The flesh of this species is thick, very firm, and white in color. Its color remains unchanging when bruised, exhibiting no staining, although there may be a slight discoloration. When sliced, the flesh appears firm and does not change color, with occasional instances of turning slightly reddish, particularly in wet weather.
Gills: The are initially whitish to pinkish when in the button stage. As they develop, they gradually transition to pale brown and eventually dark chocolate brown as they mature. They are free from the stem and can be close or crowded, with short-gills being common. During the early stages, the gills are covered with a white partial veil.
Stem: The stem can vary in length from 2 to 10 cm, with a thickness ranging from 1 to 3 cm (occasionally up to 4 cm). They are very firm, solid, cylindrical, and of equal in width or slightly thicker below, and with a narrowed or pointed base. The stems are predominantly white and typically smooth, lacking scales or any noticeable roughness. However, occasional specimens may exhibit fine, appressed scales at the apex.
This species exhibits a distinctive partial veil on its stem that is membranous, thick, and white in color. It forms a prominent and persistent ring on the stalk. This ring can take on different forms, being band-like with the upper edge free or flaring, or sheath-like resembling a volva, where only the upper edge is free. In some cases, there may be double ring is observed. This membranous double ring persists throughout the mushroom’s development, leaving a notable feature.
Spores: The spores of Agaricus bitorquis measure approximately 5-7 x 4-5.5 microns. They are smooth, elliptical, and chocolate brown in color. Furthermore, spores have thick walls and exhibit a brown color in KOH solution, with a pale apiculus that provides a contrasting shade. Similarly, in Melzer’s solution, the spores also have a brown color.
Spore Print: The spore print of this species is dark/deep chocolate brown.
Smell: This species is purported to have a mild, non-distinctive earthy odor.
Flavor and Edibility: Most mycological sources and field guides regard A. bitorquis as a choice edible due to its substantial size, a firm texture, and a delicious mushroomy flavor. Unfortunately, even the young specimen of this this species are riddled with maggots. As such some caution against consuming these mushroom is advised, unless completely maggot-free specimens are gathered.
Habitat: This species is saprobic growing alone, scattered, or gregariously in hard-packed soil along roadsides, sidewalks, parks, ditches, as well as in between cracks in concrete and gaps between paving slabs. Interestingly, these mushrooms have a tendency to fruit underground, with only the top of the cap being visible. In colder regions, they can be found along roads where salt is sprayed during winter.
Range: Agaricus bitorquis is widely distributed throughout North America, and can also be found in Europe, Asia, and Australia.
Fruiting Season: Depending on regional climate, this species can be found throughout fall, winter, and/or spring.
Agaricus bitorquis can be recognized by its short, compact, stature, firm, smooth, white to dirty-white cap, free gills, chocolate brown spores, partially emergent fruiting bodies, and love for hard-packed soils. These characteristics help distinguish this species from other Agaricus mushrooms.
The following are the species of mushroom that A. bitorquis may be confused for:
- Agaricus bernardii: This species has a contrasting habitat to that of A. bitorquis. It also has a characteristic mild briny odor, has a cap surface that often breaks up into scales or warts, and its flesh bruises red when damaged.
- Agaricus campestris: This species has a larger single ring instead of distinctive double ring. It also tends to have a lighter cap color and it is usually taller.
Toxicity and Safety[vi]
Agaricus bitorquis is generally considered safe for human consumption, and is recognized as a choice edible mushroom in several mycological sources. However, two aspects should be considered when gathering and consuming this species:
- As a partially-subterranean species A. bitorquis has the potential to accumulate toxic heavy metals, particularly lead, from areas that are contaminated or polluted. Therefore, it is crucial to avoid collecting mushrooms from sites that may pose a risk of heavy metal bioaccumulation.
- As mentioned above, It is important to be aware that specimens of A. bitorquis are frequently riddled with maggots, with small larvae commonly found inside the mushroom caps. The presence of maggots can pose potential health concerns. Therefore, it is crucial to carefully inspect and clean each specimen to remove any maggots or their eggs.
[i] Davis, R. M., Sommer, R., & Menge, J. A. (2012). Agaricus bitorquis. In Field Guide to Mushrooms of Western North America (pp. 222–223). University of California Press.
[ii] D. Arora (1986) Agaricus bitorquis (Banded Agaricus; Urban Agaricus). In “Mushrooms Demystified: A Comprehensive Guide to the Fleshy Fungi,” (pp. 321–322). Ten Speed Press, Berkeley
[iii] Kuo, M. (2017, December). Agaricus bitorquis.
[iv] Wood, M. Stevens, F. (2010). California Fungi – Agaricus bitorquis.
[v] First Nature. Agaricus bitorquis (Quél.) Sacc. – Pavement Mushroom
[vi] Lincoff, G. (1981). Spring Agaricus: Agaricus bitroquis (Quél.) Sacc. In National Audubon Society Field Guide to North American mushrooms (pp. 503–504). Knopf.