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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, making up around 30 genera.
This seaweed grows in underwater forests, in shallow, clear waters cooler than 68°F (20°C), where it grows rapidly and offers food and protection for other marine life. Many people recognize kelp from 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. The seaweed 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 seaweed, is a primary ingredient in glass and soap. Alginate, a carbohydrate harvested from it, is used as a thickening agent in toothpaste, ice cream, jelly, and other products. Some species are also used in certain cuisines, particularly in Japan, 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 are often used to wrap sushi and other foods. It 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 material. Scottish Highlanders displaced from their traditional farmlands throughout the 18th and 19th centuries sometimes turned to harvesting the ash to make a living. Though the industry eventually collapsed, kelp remains a commonly used fertilizer in Scotland.