Paxillus

Paxillus is a genus of mushroom-forming fungi in the family Paxillaceae, within the order Boletales. The genus comprises several described species native to temperate regions of Europe, Asia, and North America. Most Paxillus species are ectomycorrhizal, forming mutualistic associations with trees such as oaks, beeches, birches, and pines.

Morphology varies by species but generally includes medium-sized mushrooms with a convex to depressed cap, often brown to reddish-brown in color. The caps may be velvety or smooth and can measure several centimeters across. A distinguishing feature is the gills, which are decurrent, running down the stem, and tend to become brownish as the spores mature. The stem is typically slender and can be pale to brown, sometimes with a darker base. The flesh is usually light-colored and the spores are brown.

Ecology and habitat: Paxillus species fruit in autumn in forested areas, commonly on the ground among leaf litter or under trees in temperate woodlands. They form ectomycorrhizal relationships with their tree hosts, contributing to nutrient exchange between the soil and the roots.

Toxicity: The most well-known member, Paxillus involutus, is widely regarded as poisonous to humans. Ingestion can cause severe illness with delayed onset and may be fatal in some cases due to an autoimmune-type reaction that can be triggered or worsened by subsequent exposures. Because of these risks, Paxillus involutus should not be consumed, and caution is advised with other species in the genus, whose edibility is uncertain.

Notes: Taxonomy within Paxillus has undergone revision over time, and species boundaries can be complex. Foraging and identification should rely on expert guidance when handling unknown Paxillus specimens.