Halymeniales is an order of red algae belonging to the class Florideophyceae and the subclass Rhodymeniophycidae.

The type species is Halymenia C.Agardh.

The red algae colour comes from photosynthetic pigments (phycoerythrin, phycocyanin, allophycocyanin). Then the various blends of relative amounts of these 3 and chlorophyll, influences the plant colour, which can vary from dark red to blue, brown, or greenish.

...