Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Tripleurospermum maritimum
Tripleurospermum maritimum (syn. "Matricaria maritima") is a species of flowering plant in the aster family commonly known as false mayweed or sea mayweed. It is found in many coastal areas of Northern Europe, including Scandinavia and Iceland, often growing in sand or amongst beach pebbles.