Seaweeds are multicellular marine algae popularly named for their seeming similarity to terrestrial weed species. The fronds and the holdfasts that anchor many of the more advanced types of seaweed in place at first appear similar to the leaves and roots of some land plants, but do not carry out all of the same functions. Seaweeds occur in several different colors, including red, brown, and green, and a wide range of sizes, from only a few inches to more than one hundred feet long. Despite their disparaging name, which is suggestive that the algae are undesirable or troublesome, many seaweeds are highly useful to humans. Certain species are extremely nutritious sources of food, while others have been utilized in such diverse applications as upholstering, curing leather, and the production of cosmetics, paper, and pharmaceuticals.