Seaweed = algae = marine algae

Most of us unknowingly eat processed sea vegetables every day.  Manufacturers use them as thickeners and stabilizers in such products as ice cream, instant pudding, whipped toppings, salad dressings, and even toothpaste. They're dense with vitamins, minerals, and protein, yet low in calories. You can usually find  dehydrated sea vegetables in the Asian foods section of larger supermarkets.  After dehydrating, chop them up and add them to salads, soups, stews, or stir-fries.

Hair vegetable = black moss = hair seaweed = hair-like vegetable = fat choy 

The Chinese add this to soups and use it as a garnish.  Look for it in Chinese markets and pharmacies.
 

Hijiki = hiziki  =Hijik (Japanese)

This Japanese seaweed has a mild flavor is similar to wakame, so it's a good choice if you want to slip a sea vegetable unobtrusively into your soups and stews in order to fortify them with calcium, iron, and other nutrients. It is available dried and roughly quadruples in size and finely shredded, so a little goes a long way.

Konbu = kombu (Japanese) = tangle = sea tangle = oarweed = sea cabbage = kelp (English) =Haidai (Chinese)  

Several types of seaweed are used in Asian cooking, especially in Japan and Korea. The most common variety is the giant seaweed known as kelp in English. It is only available in dried form in strips or sheets in the West, usually labeled with the Japanese name of kombu or konbu. Choose konbu that's very dark, almost black, and don't wipe off the white residue that often appears on the surface; it's very flavorful.

Kombu is full of vitamins and minerals, and is particularly rich in iodine. It has a strong "sea" flavor and a crunchy texture.

This type of seaweed is mainly used in soups in China, but served poached or stewed as a vegetable in Japan, as well as being used to flavor the fish stock known as dashi.

Sushi nori = seaweed sheets = nori (Japanese)

this is the wafer-thin dark sheets, dried seaweed that is mainly used as a wrapping for sushi.  They're usually a dark purplish-black, and almost transparent in places, but they turn green and acquire a pleasant, nutty flavor when toasted. Ready-toasted sheets known as yaki-nori are available from Asian stores. These are seasoned with ingredients such as soy sauce, salt and sesame oil.

Wakame (Japanese)= alaria

This young dark-colored seaweed has a delicated flavor and soft but crisp texture. It has a sweet flavor, and it's rich in calcium.  It is available shredded, fresh (vacuum-packed) or dried, and is used in soups and salads. It's often dehydrated and then added to miso soup or sautéed as a side dish.  Dry wakame can also be toasted and crumbled over salads and other dishes. Dried wakame should be soaked in tepid water for 10-15 minutes until it softens and the fronds turn green. At this stage it should be drained, blanched in boiling water for about 1 minutes, then refreshed under cold water and drained again.

Agar-Agar = Dongfen = Yangcai (Chinese) = Kanten (Japanese)

This is the gelatinous substance obtained from the seaweed know as "rock-flower vegetable" in Chinese. Available from Thai or oriental stores as long dried strips or as a fine white powder sold in tubs, it is a very popular setting agent, especially for vegetarians seeking an alternative to gelatin.

Agar-agar has no aroma and is entirely flavorless, but will absorb the seasonings with which it is prepared.

Asian cooks sometimes use soaked strips of agar-agar in a salad, just as they would any other form of seaweed, but it is more often used as a setting agent, usually to make sweet jellies.