Hygrophorus agathosmus

''Hygrophorus agathosmus'', commonly known as the gray almond waxy cap or the almond woodwax, is a species of fungus in the family Hygrophoraceae. It was first described by Elias Magnus Fries in 1815; Fries gave it its current name in 1838. A widespread species, it is distributed in the United States, Europe, Africa, and India, and is found growing under spruce and pine in mixed forests. The fruit bodies are characterized by a light grayish cap that measures up to in diameter, waxy gills, a dry stem, and the distinct odor of bitter almonds. An edible but bland-tasting mushroom, extracts of the fruit bodies have been shown in laboratory tests to have antimicrobial activity against various bacteria that are pathogenic to humans.

Taxonomy, classification, and naming

The species was originally named ''Agaricus agathosmus'' by Swedish mycologist Elias Fries in 1815; he later moved it into the genus ''Hygrophorus'' in 1838. In the interim, English naturalist Miles Joseph Berkeley named the species ''Agaricus cerasinus'' in 1836, although he too would later transfer the species to ''Hygrophorus'' in 1860. In 1948, Richard Dennis examined the type material, and concluded that the two names referred to the same species. Additional historical synonyms include ''Limacium pustulatum'' var. ''agathosmum'' (Kummer, 1871), and ''Limacium agathosmum'' ( Wünsch, 1877).

In their 1963 monograph of the ''Hygrophorus'' of North America, American mycologists Lexemuel Ray Hesler and Alexander H. Smith classified ''H. agathosmus'' in the subsection Camarophylli, a grouping of related species characterized by a dry stem, and the absence of a gelatinous outer veil.

The specific epithet ''agathosmus'' is derived from the Greek word ''agathos'' meaning “good”, and ''osme'' meaning “scent”. ''Hygrophorus agathosmus'' is commonly known as the gray almond waxy cap, or the almond woodwax.

Description

The cap is in diameter, and initially convex with the edges rolled inwards. As it ages and the cap expands, it becomes flat, sometimes with the center slightly depressed, or sometimes with a slight central elevation. The color is a dull ashy gray, and when moist, the cap surface is sticky or tacky to the touch. It is smooth, although the edges can have a layer of minute, soft hairs. The flesh is soft, and whitish or watery gray. ''Hygrophorus agathosmus'' has a pronounced fragrant odor resembling cherry pits or bitter almonds (occasionally the odor is weak).

The gills have an adnate attachment to the stem, but in maturity the attachment becomes adnate-decurrent, meaning the gills start to extend down the length of the stem. The gills are white, but become grayish in maturity, close to distant (40–50 reach the stem), moderately narrow, rather thin. The stem is long by thick, whitish at first, and colored pale ashy in age. It is the same thickness throughout or somewhat narrowed toward the base. It is solid, dry or moist but has no gelatinous universal veil present. When young, the stem surface is evenly covered with tiny fibrils and a fine whitish powder; over time it loses the hairs and the powder and becomes smooth.

Microscopic characteristics

When viewed in mass, such as with a spore print, the spores appear to be white. Viewed with a light microscope, the basidiospores are 8–10.5 by 4.5–5.5 μm, ellipsoid, smooth, and yellowish in Melzer's reagent. The spore-bearing cells, the basidia, are four-spored and measure 48–65 long by 6–8 μm thick. Pleurocystidia and cheilocystidia (specialized cystidia found on the gill faces and edges, respectively) are absent in this species. The pileipellis (cap cuticle) is made of a broad (175–350 μm) gelatinous zone, composed of loosely interwoven, slender (1.5–4 μm) hyphae; the surface hyphae are a fuscous