-Kelp, Diatoms, and Allies (Kingdom Chromista)

-Phylum Ochrophyta

-Brown Algae (Class Phaeophyceae)

-Subclass Fucophycidae

-Order Ralfsiales

-Family Ralfsiaceae

-Ralfsia (Genus Ralfsia)

Ralfsia is a genus of brown algae in the class Phaeophyceae, known for forming thin, crust-like patches tightly adhered to rocks in the intertidal zone. Unlike the familiar leafy or branching seaweeds, Ralfsia grows as a flat, encrusting film, often appearing as brown, olive, or dark greenish patches that can look like a stain or coating on the rock surface. These algae are especially common in wave-exposed shorelines, where their low profile helps them withstand strong surf and desiccation during low tide.