This phylum is the most diverse of the algae phylums. The volvox shown below is a colonial green algae. Brown algae is mainly marine and have complex structures. They get their name from the brown pigment fucoxanthin. Brown algae can be quite large and includes kelps which can grow to over 50 meters long.
Diatoms are unicellular and golden-brown in color.
They are photosynthetic and very important in ocean food chains because of their rapid reproduction rates.