ABSTRACT
Today, algae are not a taxonomic category. However, the term is very useful for grouping both prokaryotic organisms, in which cell organelles are not delimited by membranes, and eukaryotic organisms, in which they are. Considering biochemical criteria, their ecological affi nities and common photosynthesis with oxygen production, in this chapter we will focus on both photosynthetic bacteria with chlorophyll a, division Cyanophyta, and the different divisions of eukaryotic algae.
