The genus Iridaea belongs to the Division Rhodophyta and has all of the characteristics of a good red alga. Just like the other members of this phylum, Iridaea uses Floridaean Starch as its carbohydrate storage product. Its major photosynthetic pigments include chlorophylls a and d, cartenoids, zeaxanthins, and the water soluble phycobiliproteins, R phycocyanin, allophycocyanin, and phycoerythrin. Within the Division Rhodophyta, Iridaea stands in the Subclass Florideophycidae.
Division is apical and the plant is multicellular.
Pit connections commonly connect cells. Iridaea has a triphasic life history with no flagellated stages and oogamous sexual reproduction . An alga is considered procarpial when its auxiliary cell and carpogonium lie in close proximity on the same branch system. The types of carrageenan in several genera of this family are specific to certain life history phases. Among the Gigartinales, the auxiliary cell is an ordinary vegetative filament present before zygote formation.