Sargassum fusiforme is a species of edible brown macroalga in the family Sargassaceae, native to the coastal waters of the northwest Pacific Ocean, particularly around China, Korea, and Japan. The genus name Sargassum originates from the Portuguese word sargaço, historically used for floating seaweeds encountered by sailors, while the species epithet fusiforme derives from Latin fusus (“spindle”) and forma (“shape”), referring to the spindle-like form of its branches or structures. This seaweed is widely known in Japanese as hijiki (ひじき) and has long been harvested as a traditional edible sea vegetable in East Asian cuisines.

The alga grows attached to rocky coastal substrates in shallow marine environments where it forms dense stands. It has branching, dark brown to black fronds with small cylindrical segments and leaf-like structures that aid in photosynthesis. Like other members of the genus, Sargassum fusiforme is a photosynthetic marine organism that absorbs nutrients directly from seawater. It is typically harvested from coastal reefs, then boiled and dried to preserve it for culinary use.

As a food source, Sargassum fusiforme is commonly rehydrated and cooked in dishes such as simmered vegetable mixtures, rice dishes, and side dishes in Japanese and Korean cuisine. The seaweed has a slightly sweet, earthy flavor and a firm texture after rehydration. Historically it has been valued not only for its flavor but also for its mineral content and long shelf life when dried.

Chemically, Sargassum fusiforme contains several characteristic compounds found in brown algae. Major constituents include alginate polysaccharides, fucoidan (a sulfated polysaccharide), laminarin, and the sugar alcohol mannitol. These compounds contribute to the seaweed’s texture and functional properties when cooked. It also contains iodine, calcium, magnesium, and various trace elements obtained from seawater. Brown algae additionally produce fucoidan and phlorotannins that have been studied experimentally for potential antioxidant, anti-inflammatory, and metabolic effects. However, the seaweed is also known to accumulate relatively high levels of inorganic arsenic compared with many other edible seaweeds, which has led to dietary advisories in some countries regarding frequent consumption.