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Classified as marine algae, seaweeds are chlorophyll- containing plants without true stems, roots, or leaves that live in the sea or brackish water, often attached to rocks or other surfaces. Successful and resilient species, they’ve been around for more than two billion years. Most seaweeds are photosynthetic, relying on sunlight as an energy source from which to produce food.
Although all have chlorophyll, many also contain other pigments in order to better absorb various wavelengths of light and capture more of the sun’s energy. As a result, they occur in three main color groups—red, green, and brown—which is a handy way of classifying them.
Green seaweeds, such as sea lettuce, mainly contain chlorophyll, similar to their land-based brethren.
Red seaweeds, which include dulse, laver, nori, agar, and Irish moss, primarily have red pigments, although they can look purple as well as a whole range of other related colors depending on the specific kinds of carotene pigments present. Because this class of pigments can be water soluble and heat sensitive, seaweed that looks red when uncooked may change to a dark green after cooking.
Brown seaweeds, such as kelp, kombu, alaria, arame, wakame, sea palm, and hijiki, depend on brown pigments from other carotenoid pigments, fucoxanthin in particular. Although chlorophyll is also a component of brown seaweeds, its green color is masked by the brown.
Seaweeds have long been known for their nutritional attributes.
Traditional Chinese medicinal texts as far back as 2700 BCE mention seaweed’s medicinal qualities, including reference to its ability to reduce goiter. The Ebers Papyrus, the ancient Egyptian dissertation on medical care thought to have been written in 1550 BCE, also specifically includes the therapeutic use of seaweeds, as do Ayurvedic medicinal texts from the fourth century CE.
Current scientific research has keyed in on the phytonutrients in seaweeds, including lignans that may help prevent certain forms of cancer, including breast cancer. Tumor reduction, inhibition of cancer cell proliferation, free radical scavenging, and significant antioxidant activity have also been exhibited by red and brown seaweeds.
In addition, sulfated polysaccharides, a type of carbohydrate found in some of the brown seaweeds, are being explored as antiviral agents and as aids in preventing blood clots. Studies exploring polysaccharides in bladderwrack and kelp have also shown them to be a highly effective agent for reducing the effects of radiation toxicity.
With their ocean origins, sea vegetables are a valuable source of a wide array of trace minerals and, depending on the variety, small amounts of calcium, magnesium, and potassium.