Aspropaxillus giganteus
Aspropaxillus giganteus, formerly Leucopaxillus giganteus, commonly known as the giant leucopax or the giant funnel, is a saprobic species of fungus in the order Agaricales. As its common names imply, the fruit body, or mushroom, can become quite large—the cap reaches diameters of up to. It has a white or pale cream cap, and is funnel-shaped when mature, with the gills running down the length of the stem.
The species has a cosmopolitan distribution and is typically found growing in groups or rings in grassy pastures, roadside hedges, or woodland clearings. It is considered by some to be a choice edible when young, and has been shown to contain a bioactive compound with antibiotic properties.
Taxonomy
The species was first described as Agaricus giganteus by English naturalist James Sowerby in 1809, who illustrated it in his book Coloured Figures of English Fungi. Other historical synonyms include Clitocybe gigantea, Paxillus giganteus, and Omphalia geotropa var. gigantea. In 1934, Robert Kühner and Réné Maire created the genus Aspropaxillus to contain species of Leucopaxillus with smooth spores, and they set L. giganteus as its type species. American mycologist Rolf Singer transferred it to genus Leucopaxillus in 1938, but recognized the value of maintaining a distinction of the smooth-spored species, and so made L. giganteus the type species of section Aspropaxilli.In 2012, Vizzini et al. showed that Leucopaxillus in its then-current definition was polyphyletic. And Leucopaxillus giganteus, not belonging to Aspropaxillus s.s., moved back to genus Aspropaxillus.
Aspropaxillus giganteus is commonly known as the 'giant leucopax' or the 'giant funnel'.
Description
The cap can become rather large, ranging from, rarely even in diameter with a thickness of at half the radius. The cap is initially convex with an inrolled margin, then flattens out and becomes shallowly funnel-shaped. The cap is smooth and creamy white in color, but may develop brown stains and circular cracks with age.The cream-colored gills are narrow, crowded close together, and have a decurrent attachment—running down the length of the stem; in age the gills will darken to a buff color. The stem is off-white with reddish-brown fibers and has dimensions, when mature, of tall and thick. There is no ring on the stem. At the base of the stem there is typically a dense, white mycelium that may form a mat. The flesh is firm, and also is white. Mature specimens are fragile, and difficult to remove from the ground without breaking.
Microscopic characteristics
When viewed in deposit, such as with a spore print, the spores appear white. When viewed with a light microscope, the spores are ovoid to ellipsoid, translucent, have a smooth surface, and possess a broadly rounded apex and base; the spore dimensions are 6–8 by 3.5–5 μm. The spores of A. giganteus are amyloid—meaning that they will absorb iodine when stained with Melzer's reagent—however, the extent of the stain may be variable. The spore-bearing cells, the basidia, are 25–40 by 4.5–8 μm, narrowly club-shaped, and are attached to either 2 or 4 spores. The hyphae of this species invariably have clamp connections.Similar species
Aspropaxillus giganteus somewhat resembles A. candidus, but the latter species has a darker coloring and is found more commonly in montane regions. Aspropaxillus septentrionalis is also large and resembles A. giganteus at some points during its development, but may be distinguished by its nauseous odor, the tan color of the cap, and the adnate to slightly adnexed gills. A. candidus tends to be smaller, with a cap diameter ranging from broad. Leucopaxillus albissimus, Leucopaxillus gentianeus, Lactifluus vellereus, and Infundibulicybe gibba have been suggested as additional lookalike species. Young specimens of A. giganteus may be confused with Lepista irina, Clitocybe praemagna or C. robusta. White Lactarius and Russula species may also appear superficially similar, but they have brittle flesh that breaks cleanly, unlike the fibrous flesh of A. giganteus.Habitat and distribution
Aspropaxillus giganteus can form fairy rings in grassy areas like pastures, and is also found along roadsides; it produces fruiting bodies in summer and autumn. It is a saprobic species, and so derives nutrients by decomposing organic matter.The fungus has a cosmopolitan distribution, and occurs throughout the temperate zone of the northern hemisphere. It is found in North America, Britain, and Europe. David Arora reports that in North America, it is most common in the Pacific Northwest and the Rocky Mountains.