Sargassum spp.
Phaeophyta, Sargassaceae
Authority: C. Agardh
Hawaiian name: limu kala ('to loosen' or 'to forgive')
Characteristic feature: Leathery brown alga with leaf-like appendages, often with vesicles or 'floats'.
Description: Plants arising from conical or shovel-shaped base, with short erect stem or axis from which several to many primary branches given off, these forming secondary branches as laterals; if primary branches become leading axes, then plants elongate and rather circumscribed in outline; if secondary branches become leading axes, then plants usually bushy with short and long second- and third-order axes that form pyramidal to uneven outlines. Leaflike appendages extremely variable in size and shape, varying margins such as toothed, dentate, smooth, undulate, twisted, duplicate, with midribs, and sterile hair pits on the surface; axes smooth or spiny, spines coarse or thin, closely set or well spaced; when growing in deeper water, plants often with vesicles ("floats") that help suspend upper plant parts in the water column; vesicles of various rounded, ovate or oval shapes, with or without terminal 'leafy' appendages. Reproductive organs, oogonia and antheridia usually collected in conceptacles, these aggregated into receptacles.
Habitat: Mid to low rocky intertidal areas, including tidepools, with at least moderate wave action and on reef flats. Has been dredged from 200 m depth. Often found near areas where fresh water mixes with ocean water.
Hawaiian distribution: All main Hawaiian Islands, including the Northwestern Hawaiian Islands.
Other: Used for food, medicine, ceremony including special hula dances. The Hawaiian name was derived from one of Sargassum's ceremonial uses, a forgiveness ceremony (ho‘o pono pono) held by families or individuals who are quarrelling.
Three of the four endemic Hawaiian species of Sargassum are common in Hawaiian waters. S. echinocarpum has main branches with conspicuous spines and shorter, wider leaves with dentate margins. S. polyphyllum is bushy in appearance, and can be distinguished by its spiny branch axes. S. obtusifolium has narrow and often needle-like leaves.