Fruiting body annual; sessile to substipitate, consisting of overlapping, rounded fleshy shelves, 7-55 cm broad, upper surface smooth to roughened, yellow with reddish-orange to orange bands, margin yellow, irregular; flesh 2-3 cm thick, white to yellow; lower surface finely pored, bright yellow; in age fruiting body becoming dry, white and crumbly.
Spores 5-7 x 4.0-5.0 µm, oval, smooth. Spore print white.
Late summer to early fall on logs and stumps of hardwoods. It is particularly common on species of Eucalyptus.
Edible with caution. Prized by many, this species is also known to cause gastrointestinal upsets. Controversy exists whether the upsets are caused by old specimens, improperly cooked specimens, specimens growing on certain trees (Eucalyptus has be mentioned as a suspect host), or some other cause. If you decide to try it, eat only the young, fresh, growing margins, in small quantities, and cook it thoroughly.
The brilliant yellow-orange, fleshy shelves of Laetiporus gilbertsonii are unlikely to be mistaken for any other fungus. The sulphur shelf is unusual in that it fruits well before the start of Bay Area rainy season, often in very dry weather. Nonetheless, fruitings, which can be massive, can literally exude moisture. The brightly-colored shelves persist several weeks, then fade to greyish-white, crumble and fall to the ground. Old fruitings on Eucalyptus are frequently infested with termites. Fruitings repeat year after year from the same stump or log.
Our sulphur shelf has long known locally as Laetiporus sulphureus. But we now know that the true L. sulphureus does not occur in the Western United States and that the sulphur shelf that grows on hardwoods in California needs the new name L. gilbertsonii. The sulphur shelf that grows conifers in California is now called Laetiporus conifericola. In the Sierras it is very common on red fir (Abies magnifica).