The taxonomic significance of the polysaccharide structures of algal cell walls has been underscored several times over the past few decades but has never been pursued systematically. Many changes in red algal systematics and the biochemical analyses of phycocolloids have occured in recent years. The cell‐wall composi‐tion of representatives of 167 (24.7%) genera and 470 (11.5%) species of red algae has been documented.The method developed by Chopin and Whalen for carrageenan identification by Fourier transform infrared diffuse reflectance spectroscopy is extended to the study of phycocolloids for diverse species in many red algal orders. This paper focuses on the Gigartinales in which representatives of 28 (68.3%) families, 88 (50.6%) genera and 224 (27.9%) species have been analyzed. In light of recent molecular phylogenies, some patterns of distribution of key phycocolloid attributes, corresponding to familial and ordinal level groupings, are emerging; however, more species remain to be analyzed. The well‐documented biochemical alternation of generations in the Phyllophoraceae, Petrocelidaceae and Gigartinaceae still holds (with two exceptions), but this pattern was not recorded in other families of Gigartinales.

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