A stroll along the coastal bluff reveals little yellow flowers peeking from beneath the sagebrush and scattered across the grassland. Each handful of blossoms is scattered across a mounded patch of three-parted (cloverlike) leaves. This is hairy woodsorrel, or Oxalis albicans. The lemon-yellow petals splay outward around a hub of stamens like stout spokes on a cart wheel. If you nibble a leaf you’ll find the refreshing tartness that is characteristic of the sorrels.
Even the petals of hairy woodsorrel have a few minute hairs, and the leaves are distinctly hairy. This little flower is a native that is found only in coastal California–but it has a similar-looking cousin (O. corniculata) which is non-native and invasive; a common garden weed. Recognize the native hairy woodsorrel, which likes to grow near the coast, because it has slightly large petals (8-12mm long). O. albicans also does not grow roots at the leafy nodes of its stems, and its taproot is woody instead of fleshy (another name for our native is radishroot woodsorrel). 
Flowers Of Marin 