About Agaricus californicus Peck
Agaricus californicus Peck has caps 5–12 cm (2.0–4.7 in) wide; the caps are white, sometimes with a grayish-tan center, and dry. They either stay unchanged or yellow slightly when bruised. The stalk is 3–10 cm (1.2–3.9 in) long and 1–2 cm wide, and may be larger at the base. It bears a persistent ring. Its spores are brown and smooth. Like many species in Agaricus section Xanthodermati, this species shows a reaction where damaged flesh turns yellow, then darker, though this reaction is not always easy to see. The cap surface turns yellow when exposed to KOH. This species is mildly poisonous, and causes gastrointestinal upset in many people. The cause of these symptoms is unclear, and some people can eat it without any symptoms. Because there is no way to know who can eat this mushroom safely, consumption is generally not recommended.
