Lacy mounds of flat, greenish-brown leaves stand out in the cacophony of intertidal life. This is rockweed (Fucus gardneri), another brown alga that is widespread from Alaska to California. The mature tips puff up and act as a float–and as the nursery where sperm and eggs develop before being released to find one another in the water. These tips are edible, and were called “Indian popcorn” by settler because local tribes liked to eat them dried. Other sources recommend eating them young (either fresh or blanched); but always in moderation.
Other names for rockweed include bladderwrack and popweed. It has several lookalikes (F. spiralis, Hesperophycus californicus and Pelvetiopsis limitata), but rockweed can be identified by the central midrib running down each hairless, mitten-shaped leaf.
Flowers Of Marin 