Marine Animal Encyclopedia
Sea palm Postelsia palmaeformis
Sea palms are kelps, which are large brown seaweeds that belong to the order Laminariales. Unusually for a kelp, sea palm grows on the midshore, where it forms dense stands on wave-exposed coasts. It has a branched holdfast, and a stout, hollow stalk, which stands erect when the tide is low. The top of the stalk is divided into many short, cylindrical branches, each of which bears a single frond up to 10 in (25 cm) long, with toothed margins and deep grooves running down both faces. Spores are released into the grooves and drip off the frond tips onto the holdfasts and nearby rocks at low tide, so that the developing seaweeds grow as dense clumps. Some Sea palms attach to mussels and are later ripped off during storms, making more rock available for other sea palms to grow.