Seaweeds, including kelp, do not have roots. The gnarled structures attaching this giant seaweed to the rock is the kelp's holdfast. Kelp grow on rocky bottoms, not sandy shores. Their holdfasts are tangled to cling tightly to the rocky substrate.

Photograph by Tay Tousey, MyShot
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Kelp is a giant seaweed that grows in two forms along the west coast of North America—giant kelp and bull kelp.