Monterey Bay Aquarium Research Institute
Marine Botany

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Gelidium is a polymorphic genus consisting mainly of highly branched algae with morphological differences in species ranging from from terete (cylindrical) to compressed branches. Different species also show a wide range of sizes from G. pusillum which can be less than 1 cm tall to G. robustum which can reach 40 cm in height. Gelidium species are uniaxial with a dense, central medulla. Growth occurs in Gelidium as the pericentral cells originate through transverse division from the apical cell and form apical cells of lateral branches. This growth pattern results in a morphology described as monopodial branching. Species of Gelidium can vary a lot in color within and between species, from red to purple to green-black. 

Gelidium on rocksSpecific anatomical structures are used to identify Gelidium. Small, thick-walled, wiry rhizoidal filaments are found in the subcortical and outer tissue of the medulla, and these are thought to function to enhance structual stability. Cells in Gelidium contain pit plugs, a structure formed from incomplete division of the cell wall. The layers of material in the pit plugs are used as a taxonomic characteristic and species of Gelidium have a single plug cap layer. 

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© 1999 Sharon C. Komarow. All rights reserved.