About this fungus
Yellow-staining Milk Cap is a fungus in the Russulaceae family. Its habitat and field characteristics are summarised below.
A brittle western North American milkcap with a pinkish-brown, reddish-brown or orange-brown cap, usually marked by faint concentric bands and darker spots. The cap broadens from convex to almost flat or shallowly depressed. Its name refers not to an overall yellow cap, but to the vivid yellow stain produced after its white milk meets the air.
What to check
Damage several fresh gills and watch the liquid itself. It should emerge white and then turn bright sulphur-yellow quickly, staining the gills and cut flesh yellow. Check for close pale yellow to peach-buff gills that begin to run slightly down the stem and become orange-buff with age, a pale yellow spore print, and a smooth cap that is slightly sticky when damp. The cap edge is not bearded, the stem has no pits, and there is no ring or volva. The fast latex change is important, but western range, tree context and the remaining characters must agree as well.
Variation
Cap bands can be obvious or so faint that the surface appears nearly even, and colours range from pinkish cinnamon through orange-brown to deeper reddish-brown. Dark spotting may develop on the cap, while the stem ranges from pale peach to pinkish-brown. Published accounts differ on whether the flesh is only faintly acrid or distinctly peppery, so flavour is not used here as an identification test. Fresh latex behaviour is more useful than appearance in old or dried material.
Lookalikes
Lactarius alnicola occurs in the same western coastal forests but is paler, often has a woolly cap edge and pits on the stem, and its white latex changes little or only slowly towards yellow. Eastern North America's Lactarius vinaceorufescens can have a similar yellow latex reaction but develops wine-red staining and is associated especially with eastern white pine. Lactarius chrysorrheus is another eastern yellow-staining species, generally paler and linked with oak. Candy Cap, Lactarius rubidus, has a more evenly red-brown cap, watery latex that does not turn yellow and a maple-like smell when dry. Microscopy may be needed when several yellow-staining milkcaps overlap.
Habitat and range
Ectomycorrhizal in western North America, principally from coastal and low-montane California and southern Oregon into northern Baja California. It occurs with hardwoods and conifers, especially oaks, tanoak and Douglas fir, and fruits singly or in groups on the woodland floor. Fruiting is mainly in the wet autumn and winter season. Records from eastern North America or other continents should be compared carefully with related regional species rather than assigned to this name from yellow latex alone.
Food safety
Poisonous.