Redwood sorrel

Description:

Shamrock-shaped leaves, white flowers

Habitat:

shady areas under fir/hemlock/spruce/alder in a temperate rainforest

Notes:

the leaves react to the level of light, folding down when the sun is strongly on them. Locals sometimes call it "sour grass", though clearly it's not a grass; it's a favorite snack for those walking through the woods--refreshing but tangy from the oxalic acid.