Kids Research Express

The largest of the green algae, Ulva (sea lettuce), grows to a ribbon or sheet 3 ft (91 cm) long. It provides food for many sea creatures, and its broad surface releases a large amount of oxygen. Fucus, called rockweed or bladderwrack, is a tough, leathery brown alga (though it often looks olive-green) that clings to rocks and has flattened, branched fronds buoyed by air bladders at the tips. Seaweeds , especially species of the red algae Porphyra (nori) and Chondrus, form an important part of the diet and are farmed for food in China and Japan; other species (often called laver) are eaten in the British Isles and Iceland. Commercial agar (vegetable gelatin) is obtained from species of red algae and is the most valuable seaweed product. Irish moss or carrageen (Chondrus crispus), a red alga, is one of the few seaweeds used commercially in the United States. After being bleached in the sun the fronds contain a high proportion of gelatin, which is used for cooking, textile sizing, m...

Seaweed, name commonly used for the multicellular marine algae. Simpler forms, consisting of one cell (e.g., the diatom) or of a few cells, are not generally called seaweeds; these tiny plants help to make up plankton. The more highly developed types of seaweed usually have a basal disk, called a holdfast, and a frond of varying length and shape, which often resembles a plant in having stemlike and leaflike parts. Types of Seaweed The simplest of the seaweeds are among the cyanobacteria, formerly called the blue-green algae, and green algae (division Chlorophyta), found nearest the shore in shallow waters and usually growing as threadlike filaments, irregular sheets, or branching fronds. The brown algae (division Phaeophyta), in which brown pigment masks the green of the chlorophyll, are the most numerous of the seaweeds of temperate and polar regions. They grow at depths of 50 to 75 ft (15–23 m). The red seaweeds (division Rhodophyta), many of them delicate and fernlike, are found...