Cystoseira tamariscifolia is a bushy seaweed, up to 60 cm in length but usually 30-45 cm. It has a cylindrical frond and branches irregularly. The reproductive bodies on the end of branches are long, oval and spiny. Small air bladders are usually found below the reproductive bodies. Cystoseira tamariscifolia is olive green in colour, almost black when dry. When the plant is seen underwater it has a blue-green iridescence.