Leathesia difformis

Other brown algae that grow along the coast include the sea cauliflower (Leathesia difformis), which lives atop the fronds of other plants, and the sea palm (Postelsia palmaeformis), a stalklike plant that resembles a palm tree. Sea palms can grow on top of mussels, increasing the likelihood that the small animals will be uprooted from their positions by wave action. When this happens, the vacancy on the substrate created by a mussel s departure is quickly filled by another sea palm. 

Feldman, S. C., Reynaldi, S., Stortz, C. A., Cerezo, A. S., and Damont, E. B. (1999). Antiviral properties of fucoidan fractions from Leathesia difformis. Phytomedicine 6, 335-340. 

---