Any of a genus (Sargassum, family Sargassaceae) of floating brown algae (order Fucales) found in tropical seas and having a main stem with flattened outgrowths like leaves, and branches with berry-like air sacs; gulfweed.
In the North Atlantic this region is covered by enormous banks of gulf-weed (Sargassum bucciferum), hence the name Sargasso Sea.
In Fucus vesiculosus they arise in lateral pairs; in Ascophyllum they are single and median; in Macrocystis one vesicle arises at the base of each thallus segment; in Sargassum and Halidrys the vesicles arise on special branches.
Some of these ancient seaweeds may have remained permanently rooted in the littoral regions, while others may have become broken off and drifted, like the recent Sargassum, at the mercy of the winds and currents, carrying the attached Graptolites into all latitudes.
Porphyra laciniata, the edible laver; Codium tomentosum, a coarse species; Padina pavonia, common in shallow water; Ulva latissima; Haliseris polypodioides; Sargassum bacciferum; the well-known gulf weed, probably transported from the Atlantic; Zostera marina, forming dense beds in muddy bays; the roots are cast up by storms and are valuable to dress the fields.