Kelp is a type of seaweed or algae belonging to the order Laminariales. Though its appearance is similar to that of plants, it is technically not a plant, but a protist. There are many different kinds of kelp, constituting around 30 genera.

Kelp grows in underwater kelp forests, in shallow, clear waters cooler than 68¡ãF (20¡ãC). It grows rapidly and offers food and protection for other marine life. Kelp is recognizable as the seaweed you may have seen on a trip to the beach. It is anchored to the ocean floor by a structure known as a holdfast, and most of its body resembles a stem with leaves, correctly termed a stipes with blades. Kelp also features air-filled bladders that allow the rest of the body to float and bring the leaf-like blades to the surface of the water.

Humans throughout history have found many uses for kelp. Soda ash, once produced by burning kelp, is a primary ingredient in glass and soap. Alginate, a carbohydrate harvested from kelp, is used as a thickening agent in toothpaste, ice cream, jelly, and other products. Some species of kelp are also used in certain cuisines, particularly Japanese cuisine, or as an organic fertilizer.

Kelp is a very versatile ingredient in food. It can be used as a flavoring, a garnish, a vegetable, or a snack food. Dried sheets of kelp are often used to wrap sushi and other foods. Kelp has a distinctive taste and is both decorative and flavorful.

Though soda ash can now be produced in a lab, kelp was once the world's major source of the mineral. Scottish Highlanders displaced from their traditional farmlands throughout the 18th and 19th centuries sometimes turned to kelp ash harvesting to make a living. Though the industry eventually collapsed, kelp remains a commonly used fertilizer in Scotland.