Agrocybe putaminum

🏷️ Description

If you’ve ever strolled through a park or garden and spotted a velvety, brown-capped mushroom sprouting from woodchips, you might have encountered Agrocybe putaminum, also known as the Mulch Fieldcap. This intriguing fungus thrives in urban landscapes, making itself at home in woodchip mulch, garden soil, and other lignin-rich environments.

📜 A Mushroom with a History: Described as new to science in 1913 by French mycologist René Maire, this species was initially named Naucoria putaminum after being discovered in garden soil covered with plum stones. In 1936, Rolf Singer reclassified it under the genus Agrocybe, where it resides today. Once considered rare, its distribution has expanded, thanks to the widespread use of woodchip mulch in landscaping.

🔎 Identification

• Cap: Convex at first, then flattening with age, sometimes developing a shallow bump in the center. It starts out dark brown but fades to a yellowish-tan hue over time. The matte, velvety surface is lightly pruinose (as if dusted with fine flour). Size ranges from 3–10 cm (1.2–3.9 in) in diameter.

• Gills: Initially pale clay-brown, becoming dark brown as spores mature. They are adnate (broadly attached) to notched and moderately crowded.

• Stem: Cylindrical, 5–8 cm (2.0–3.1 in) long, 1–1.5 cm (0.4–0.6 in) thick, and slightly thicker at both the top and the base. The surface is covered in fine ridges and darkens when handled but lacks an annulus (ring).

• Flesh: White, up to 1.5 cm (0.6 in) thick, and does not change color when cut.

• Odor & Taste: Farinaceous (like freshly ground flour) with a bitter, cucumber-like aftertaste. 🍞🥒

• Spore Print: Dark brown.

• Microscopic Features: Thick-walled, elliptical spores (10–12 by 5–9 μm) with a germ pore; club-shaped, four-spored basidia; caulocystidia on the stipe, giving it a velvety feel.

👀 Look-Alikes

• Agrocybe praecox: Similar but has a paler, less velvety cap and a conspicuous annulus.

• Agrocybe smithii: Found in eastern North America, distinguishable microscopically by its larger cystidia.

• Agrocybe hortensis: Lacks pleurocystidia and has broader cheilocystidia.

🌍 Where It Grows

This saprobic species thrives in parks, gardens, and roadsides, particularly where woodchips or other woody debris are present. Originally rare, it has become more common in western North America, Europe, and parts of Australia and India. Its presence has increased in tandem with urban landscaping trends.

🍽️ Edibility

Though not toxic, Agrocybe putaminum is classified as inedible due to its bitter taste and unappetizing texture. Best to admire it rather than add it to your dinner plate!

Photo sources:

Photo 1 - Author: Brian R Wilson (CC BY 4.0)

Photo 2 - Author: Hunter H (CC BY 4.0)

Photo 3 - Author: Katherine Scott (CC BY 4.0)

Photo 4 - Author: Justin (CC BY 4.0)