Monostroma kuroshiense
Endemic green seaweed of Japan's Kuroshio Coast, cultivated for sushi wraps.
Monostroma kuroshiense is a green alga from the Chlorophyta division, found only along Japan’s Kuroshio Coast. In Japanese, it goes by Hitoegusa or Hirohano hitoegusa (ヒロハノヒトエグサ). It was once classified as Monostroma latissimum, but recent multilocus phylogenetic work showed it to be a distinct species, named after the Kuroshio Current by phycologist Felix Bast. This high-value seaweed is farmed commercially in East Asia and South America to make “hitoegusa-nori” or “hirohano-hitoegusa nori,” a popular sushi wrap. Monostroma oligosaccharides, specifically those with a degree of polymerization of 6, derived from Monostroma nitidum polysaccharides via agarase digestion, have proven effective as a prophylactic against Japanese encephalitis virus in lab and animal tests. The sulfated oligosaccharides from Monostroma are considered promising antiviral candidates. Among green seaweeds, Monostroma is the most widely cultivated genus.
Regarding its life history, extensive peer-reviewed research covers the ecophysiology of this genus. Natural and farmed sexually reproducing samples, along with sexually reproducing and accidentally discovered asexual ecotypes from Tosa Bay, Japan, all belong to the same species. Seasonal changes in thallus length vary by habitat and repeat yearly. Thalli appear and decay earlier in high-salinity habitats, suggesting salinity speeds up sporophyte maturation or gametophyte senescence. Life cycle, thallus development, gametangial formation, and phylogenetic analyses place this genus in the order Ulotrichales. The type of life cycle is not a reliable trait for defining species within Monostromataceae.
Quick Facts
- Genus
- Monostroma
- Species
- kuroshiense
Facts from the source article.
Lore & Background
Monostroma kuroshiense was previously known under the binomen Monostroma latissimum, but the latest scientific research based on multilocal phylogeny discovered it to be a new species. The algae is named after the Kuroshio Current, with naming done by phycologist Felix Bast. Natural and cultivated sexually reproducing environmental samples, as well as sexually reproducing and serendipitously discovered asexually reproducing ecotypes of monostromatic green alga from Tosa Bay, Japan, are conspecific (belong to the same species). Patterns of seasonal fluctuations in its thallus lengths were habitat specific and recur annually. Both appearance and decay of thalli were earlier at high saline habitats, suggesting that salinity positively influences either maturation of sporophytes or senescence of gametophytes. Results from life cycle, thallus ontogeny, gametangial ontogeny and phylogenetic analyses suggest that this algal genus is evolutionarily affiliated in order Ulotrichales. The type of life cycle is not a valid diagnostic character for the species circumscription in Monostromataceae.
Reader's Guide
Monostroma kuroshiense is notable as a high-value seaweed endemic to the Kuroshio Coast of Japan, where it is called Hitoegusa or Hirohano hitoegusa. Its commercial cultivation in East Asia and South America for sushi wraps underscores its economic significance. The species was reclassified from Monostroma latissimum based on multilocal phylogeny, highlighting the importance of molecular methods in algal taxonomy. The genus Monostroma is the most widely cultivated among green seaweeds, and research on Monostroma oligosaccharides—prepared by agarase digestion from Monostroma nitidum polysaccharides—has shown promise as a prophylactic agent against Japanese encephalitis viral infection in vitro and in vivo. This positions Monostroma species as potential sources for antiviral drug development. The life history studies reveal that salinity influences thallus appearance and decay, and that asexually reproducing ecotypes exist alongside sexual ones, though life cycle type is not a valid diagnostic character for species circumscription in Monostromataceae. The evolutionary affiliation with order Ulotrichales further contextualizes its phylogenetic placement.
Did You Know?
- Monostroma kuroshiense was previously known as Monostroma latissimum before multilocal phylogeny reclassified it as a new species.
- The species is named after the Kuroshio Current, with naming by phycologist Felix Bast.
- Monostroma oligosaccharides from Monostroma nitidum have shown prophylactic activity against Japanese encephalitis virus in tests.
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