Editing Brown algae (section)

===Tissue organization===

The simplest brown algae are filamentous—that is, their cells are elongate and have septa cutting across their width. They branch by getting wider at their tip, and then dividing the widening.<ref>{{cite book
|last=Wynne
|first=M. J.
|year=1981
|chapter=The Biology of seaweeds
|editor1-last=Lobban
|editor1-first=C. S.
|editor2-last=Wynne
|editor2-first=M. J.
|title=Phaeophyta: Morphology and Classification
|chapter-url=https://books.google.com/books?id=QG4tqjFPWJ0C&pg=PA52
|page=52
|series=Botanical Monographs
|volume=17
|publisher=[[University of California Press]]
|isbn=978-0-520-04585-9
|access-date=11 May 2020
|archive-date=16 October 2023
|archive-url=https://web.archive.org/web/20231016193130/https://books.google.com/books?id=QG4tqjFPWJ0C&pg=PA52#v=onepage&q&f=false
|url-status=live
}}</ref>

These filaments may be haplostichous or polystichous, multiaxial or monoaxial forming or not a [[pseudoparenchyma]].<ref name="Textbook of Algae">
{{cite book
|last1=Sharma |first1=O. P
|year=1986
|title=Textbook of Algae
|url=https://books.google.com/books?id=hOa74Hm4zDIC&pg=PA298
|page=298
|publisher=[[Tata McGraw-Hill]]
|isbn=978-0-07-451928-8
}}</ref><ref>{{Cite book|last=Graham; Wilcox; Graham|title=Algae, 2nd Edition|publisher=Pearson|year=2009|isbn=9780321603128}}</ref>   Besides fronds, there are the large in size [[parenchyma]]<nowiki/>tic kelps with three-dimensional development and growth and different tissues ([[wiktionary:meristoderm|meristoderm]], [[Cortex (botany)|cortex]] and [[wiktionary:medulla|medulla]]) which could be consider the trees of the sea.<ref>Fritsch, F. E. 1945. The Structure And Reproduction Of The Algae. Cambridge University Press, Cambridge.</ref><ref>{{Cite journal|last1=Charrier|first1=Bénédicte|last2=Le Bail|first2=Aude|last3=de Reviers|first3=Bruno|date=August 2012|title=Plant Proteus: brown algal morphological plasticity and underlying developmental mechanisms|url=http://dx.doi.org/10.1016/j.tplants.2012.03.003|journal=Trends in Plant Science|volume=17|issue=8|pages=468–477|doi=10.1016/j.tplants.2012.03.003|pmid=22513108|issn=1360-1385|access-date=13 November 2020|archive-date=16 October 2023|archive-url=https://web.archive.org/web/20231016193229/https://www.cell.com/trends/plant-science/fulltext/S1360-1385(12)00055-6?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS1360138512000556%3Fshowall%3Dtrue|url-status=live|url-access=subscription}}</ref> There are also the [[Fucales]] and [[Dictyotales]] smaller than kelps but still parenchymatic with the same kind of distinct tissues.

The [[cell wall]] consists of two layers; the inner layer bears the strength, and consists of [[cellulose]]; the outer wall layer is mainly [[algin]], and is gummy when wet but becomes hard and brittle when it dries out.<ref name="Textbook of Algae"/> Specifically, the brown algal cell wall consists of several components with alginates and [[Sulfation|sulphated]] [[fucose|fucan]] being its main ingredients, up to 40% each of them.<ref>{{Cite journal |doi=10.1016/j.tplants.2018.10.013 |title=Gazing at Cell Wall Expansion under a Golden Light |year=2019 |last1=Charrier |first1=Bénédicte |last2=Rabillé |first2=Hervé |last3=Billoud |first3=Bernard |journal=Trends in Plant Science |volume=24 |issue=2 |pages=130–141 |pmid=30472067 |s2cid=53725259 |url=https://hal.archives-ouvertes.fr/hal-02183603/file/PDF%20article%20accept%C3%A9.pdf |access-date=17 September 2022 |archive-date=8 January 2022 |archive-url=https://web.archive.org/web/20220108014851/https://hal.archives-ouvertes.fr/hal-02183603/file/PDF%20article%20accept%C3%A9.pdf |url-status=live }}</ref> Cellulose, a major component from most plant cell walls, is present in a very small percentage, up to 8%. Cellulose and alginate biosynthesis pathways seem to have been acquired from other organisms through endosymbiotic and horizontal gene transfer respectively, while the sulphated polysaccharides are of ancestral origin.<ref>{{Cite journal |doi=10.1111/j.1469-8137.2010.03374.x |doi-access=free|title=The cell wall polysaccharide metabolism of the brown alga Ectocarpus siliculosus. Insights into the evolution of extracellular matrix polysaccharides in Eukaryotes |year=2010 |last1=Michel |first1=Gurvan |last2=Tonon |first2=Thierry |last3=Scornet |first3=Delphine |last4=Cock |first4=J. Mark |last5=Kloareg |first5=Bernard |journal=New Phytologist |volume=188 |issue=1 |pages=82–97 |pmid=20618907 }}</ref> Specifically, the cellulose synthases seem to come from the red alga endosymbiont of the photosynthetic stramenopiles ancestor, and the ancestor of brown algae acquired the key enzymes for alginates biosynthesis from an [[actinobacterium]]. The presence and fine control of alginate structure in combination with the cellulose which existed before it, gave potentially the brown algae the ability to develop complex structurally multicellular organisms like the kelps.<ref>{{Cite journal |doi=10.1093/aob/mcu096 |doi-access=free|title=Chemical and enzymatic fractionation of cell walls from Fucales: Insights into the structure of the extracellular matrix of brown algae |year=2014 |last1=Deniaud-Bouët |first1=Estelle |last2=Kervarec |first2=Nelly |last3=Michel |first3=Gurvan |last4=Tonon |first4=Thierry |last5=Kloareg |first5=Bernard |last6=Hervé |first6=Cécile |journal=Annals of Botany |volume=114 |issue=6 |pages=1203–1216 |pmid=24875633 |pmc=4195554 }}</ref>