Parasitic algae is
Laminaria
Fucus
Sargassum
Cephaleuros
Cephaleuros is a genus of parasitic thalloid green algae. Its common name is red rust. The alga is parasitic on some important economic plants of the tropics and subtropics such as tea, coffee, mango and guava causing damage limited to the area of algal growth on leaves (algal leaf spot), or killing new shoots, or disfiguring fruit. Members of the genera may also grow with a fungus to form a lichen that does not damage the plants.