Kelp n. : The calcined ashes of seaweed, -- formerly much used in the manufacture of glass, now used in the manufacture of iodine.

Kelp n. : Any large blackish seaweed.

Example:
What is Kelp powder good for? Is Kelp a superfood or something?

Taxonomy
kelp, America, kelp forest, species, California, seaweeds, blades, North America, Laminaria, South America, sugars, Australia, Alaska, Tasmania, Giant kelp, Japan, free encyclopedia, Baja California.

Defination from the web:
kelp forests. ... Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate) ... The kelp life cycle involves a diploid sporophyte and haploid gametophyte stage. ...