Polynesian edible underwater plants
Limu, otherwise known as rimu, remu or ʻimu (from Proto-Austronesian *"limut") is a general Polynesian term for edible plants living underwater, such as seaweed, or plants living near water, like algae. In Hawaii, there are approximately one hundred names for kinds of limu, sixty of which can be matched with scientific names. Hundreds of species of marine algae were once found in Hawaii. Many limu are edible, and used in the cuisine throughout most of Polynesia.
Uses.
Several species of limu are used as food throughout Polynesia and is typically eaten raw as accompaniment to meals, usually fish. 
In Hawaii, limu was seen as a major component of the Hawaiian diet alongside fish and poi. Hawaiians cultivated several varieties of seaweed for food as well as to feed fish farmed within fish ponds. As many as 75 types of limu were used for food, more than the 35 used in Japanese cuisine, which is also well known for its use of seaweed. In modern times, limu is often used as a condiment, typically in raw fish dishes such as poke.
Limu was used in "hoʻoponopono", the ancient Hawaiian process of conflict resolution. Injured and accused parties gathered to pray, seek forgiveness and eat leaves as a symbol of reconciliation. It is also used in traditional hula attire and as medicine.
Due to the shape of its foliage, the Maori also applied the name to the native tree "Dacrydium cupressinum".
Types.
"Limu" comes from multiple genera 
Threats.
Limu has become increasingly difficult to find because of over-picking, pollution, and urban development, especially construction in watersheds. Many important kinds of "limu" grow best in brackish water where fresh water empties into the sea. Another threat to "limu" is the spread of marine alien invasive species, such as members of the genus "Kappaphycus ("smothering seaweed), "Gracilaria salicornia" (gorilla ogo), "Avrainvillea amadelpha" (leather mudweed), "Hypnea musciformis" (hook weed) and "Acanthophora spicifera" (prickly seaweed).
References.
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