Agaricus

Class - Basidiomycetes; Order - Agaricales; Family - Agaricaceae; Genus - Agaricus. Agaricus is a saprophytic fungus found on wood logs, manure piles, fresh litter and pastures; several species (e.g. Agaricus arvensis, Agaricus tabularis) grow in circular rings, giving them the popular name 'fairy rings', while Agaricus campestris is the common 'field mushroom'. Its vegetative structure is a mycelium built of branched hyphae, and three distinct types of mycelium appear across its life cycle: primary mycelium, which develops directly from a germinating basidiospore and is septate, uninucleate, haploid and monokaryotic; secondary (dikaryotic) mycelium, formed when two primary mycelia of opposite strain fuse; and tertiary mycelium, found specifically inside the fruiting body (basidiocarp). The dikaryotic secondary mycelium develops into hyphal cords called rhizomorphs, which can survive (perennate) in the soil for long periods, and every hyphal cell has a chitin cell wall plus organelles such as mitochondria, Golgi bodies and endoplasmic reticulum. The mature basidiocarp is umbrella-shaped, with three parts: a thick, fleshy, cylindrical stipe (stalk), whose upper part bears a membranous ring called the annulus; a broad, convex pileus (cap), usually white or cream; and, on the underside of the pileus, radiating gills (lamellae) of varying length. The stipe is hollow at the centre (loosely arranged hyphae) but its periphery is compactly arranged into pseudoparenchymatous tissue. Each gill has three regions: a central sterile trama, flanked by a compact subhymenial layer, and finally the fertile hymenium on both faces, which bears club-shaped basidia interspersed with sterile paraphyses; each basidium produces four basidiospores (two of the '+' strain and two of the '-' strain) borne on stalk-like sterigmata. Asexual reproduction occurs by chlamydospores, which germinate into mycelium in favourable conditions. Sexual reproduction has no dedicated sex organs at all: most species are heterothallic (Agaricus bisporus being a notable homothallic exception), and mycelia of opposite strain fuse directly by somatogamy to give the dikaryotic secondar …