''Sphacelaria'' is a genus of brown macroalgae (or seaweed) in the family

Sphacelariaceae Sphacelariaceae is a family of algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clade ...

Taxonomy and nomenclature

The genus and its type species (''Sphacelaria reticulata'') were briefly described by

Hans Christian Lyngbye Hans Christian Lyngbye (29 June 1782 – 18 May 1837) was a Danish priest and botanist, specialising in algae. Life Hans Christian Lyngbye was born in Aalborg, Denmark, in 1782, the son of a teacher, Jens Michelsen Lyngbye. He attended the Latin sc ...

in Florae Danicae in 1818. At the time of publication, such brief descriptions were considered to be valid by virtue of ''descriptio generico-specifica''; Lyngbye immediately added nine more species to the genus in 1819. Recent studies, however have revealed that this genus is polyphyletic, with the type species forming a separate clade with from the rest of the genus—in addition, it was also observed that ''S. reticulata'' does not exhibit the key morphological characteristics of the genus. Thus, it has been proposed to change the type species into ''S. cirrosa,'' one of the most widespread species, to conserve the genus name. Dr. Willem F. Prud’homme van Reine (1941–2020) was the foremost expert on ''Sphacelaria'' taxonomy and has contributed to the clarification and naming of the 37 confirmed species.

Morphology

''Sphacelaria'' is mainly characterized by the blackening of their cell walls when treated with bleach, polystichous (parenchymatous) filamentous thallus, hemiblastic branching (''i.e.'' laterals arise from the secondary), and leptocaulus growth (''i.e.'' uniform size of filaments, such as their mature segments have almost the same diameter as their apical ones); moreover majority of the species also have specialized branchlets for vegetative reproduction called propagules. Delineation of ''Sphacelaria'' species have been traditionally based on morphological differences, especially the variation among the propagule shape, cell dimensions, and cell arrangement of the propagules. In terms of cellular ultrastructure, ''Sphacelaria'' cells contain discoid chloroplasts and do not have pyrenoids.

Distribution

''Sphacelaria'' is a cosmopolitan genus with a majority of the species found in temperate regions but representatives also thrive in the tropics up to the arctic and antarctic areas. Species from this genus are mainly marine, however, freshwater species have been found in USA (''S. lacustris'') and China (''S.'' ''fluviatilis'').

Ecology

''Sphacelaria'' species are epiphytic and/or epilithic in nature, they form filamentous tufts or mats on the surfaces they have reclaimed and are normally found on the intertidal to shallow subtidal.

Life history

Members of this genus exhibit isomorphic (i.e., the

gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...

(N) and

sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...

(2N) stage are morphologically similar) and diplohaplontic .e., both gametophyte (N) and sporophyte (2N) generations are free-living and equally distinct bodies but only differ in chromosome number and strategylife cycle with isogamy (i.e., gametes with the same size and form) or anisogamy (i.e., gametes with different size and form). Culture studies have revealed that the reproductive strategy of ''Sphacelaria'' species are mainly dictated by the temperature, wherein propagule formation is favored during warmer seasons while sexual reproduction (i.e., formation of plurilocular and unilocular gametangia /zoidangia) occur when temperatures drop; in addition, daylength exposure is believed to contribute to the production of propagules and consequent inhibition of gametogenesis.

Exploitation, harvesting and cultivation

This genus is neither commercially nor traditionally cultivated and harvested.

Chemical composition and natural products chemistry

''Sphacelaria'' has been known to contain several natural products such as

carotene The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the ex ...

chlorophyll a } Chlorophyll ''a'' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...

, and

fucoxanthin Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. Fucoxanthin absorbs light primarily in the blue-gree ...

(the pigment responsible for the brown color of phaeophycean seaweeds). Furthermore, they also contain sulfated polysaccharides in the form of xylogalactofucan and

alginic acid Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. When the alginic acid binds with sodium and calcium ions, the resulting salts are kn ...

which have shown to have antiviral properties against the herpes simplex virus type 1 (HSV-1).

Utilization and management

This genus has been used for plant morphogenesis studies, environmental stressors research, and much of the industry interest on ''Sphacelaria'' revolves around its easy protoplast production which has implications in cellular studies involving expression profiling, RNA sequencing, and transcriptomics.

References

{{Taxonbar, from=Q21571763 Brown algae genera Brown algae