Agaricus albolutescens

Agaricus albolutescens, commonly known as the amber-staining agaricus, is a moderate-sized, stocky-statured mushroom with a pleasant odor; it bruises slowly but persistently yellow.

Taxonomy
The holotype of Agaricus albolutescens was collected at Agate Beach, Oregon, by Gertrude S. Burlingham on November 21, 1937.

Albolutescens is botanical Latin for yellowish white.

Pileus
The cap is 6–12 cm broad, and convex; it becomes planoconvex to planodepressed. The margin is incurved, then decurved, overlapping the gills. Occasionally, it is wavy and appendiculate from veil fragments. The surface is dry and white; when bruised, it turns tawny-brown. The context varies from 1.5 to 2 cm thick; it is firm and turns pale-peach when cut. When the flesh is dry, odor and taste is musty.

Lamellae
The gills are free, close, and, at first, pallid, though they then turn a pale pinkish-tan. As it ages, A. albsolutescens is dark chocolate-brown in color. The lamellulae are in five to six series.

Stipe
The stipe is 2–7 cm long, 1.5–3 cm thick, and more or less equal except for a bulbous base. In addition, it has a narrow, cottony central core. The surface of the apex is palled and finely striate, while the lower stipe can vary from glabrous to sparsely covered with whitish fibrils, occasionally sheathed with cottony-floccose veil remnants. Like the cap, it yellows. The partial veil is layered. The surface underneath can be cottony or fibrillose. Sometimes, it fragments, leaving scattered cottony patches over a membranous-tomentose basement layer. The annulus is superior, thin, and initially erect, then pendulous.

Spores
Spores are 6.0–7.5 x 4.0–5.0 μm, elliptical, and inequilateral in profile. In addition, they are smooth, moderately thick-walled, and have an inconspicuous hilar appendage. Their germ pore is absent.

Similar species
The way it bruises distinguishes the species from other members of Agaricus, such as A. xanthodermus, a mildly toxic species which has a phenolic or medicinal odor and bruises fleetingly yellow. A. albolutescens tends to discolor tawny-brown, rather than simply yellow, and the gills are chocolate-brown and free.

A. silvicola is very similar but has a less dramatic bruising reaction, more yellowish than tawny, a normal rather than stocky stature, and slightly smaller spores. A. albolutescens and A. silvicola represent a single polymorphic species or a species complex.