All photosynthetic organisms comprise of one or more organic pigments that are capable of absorbing visible, radiations, which will initiate the photochemical reaction of photosynthesis. The three major classes of pigments found in plants and algae are the chlorophylls, the carotenoids and the phycobilins.
Carotenoid and phycobilins are called accessory pigments since, the quanta absorbed by theese pigments can be transferred to chlorophyll.
The diversity of light harvesting pigments in alga implies that the common ancestor was primitive and that no close affinity exist between blue, green, red, brown, golden brown and green algae.