Tanoak (Lithocarpus densiflorus) is not an oak, but a close relative. It has large, leathery leaves with marked parallel lateral veins, and bears acorns that have bristled or spiked caps. It is one of the only acorn bearing trees that is frequently found in redwood forests.
Tanoak is highly susceptible to sudden oak death. The functional loss of this species from redwood ecosystems is a concern, as many animal species in the redwood forest are dependent upon its acorn crop.