Though the prokaryotic "cyanobacteria" (formerly referred to as "blue-green algae") were included as "algae" in older textbooks, it is not now. The term "algae" is now used for eukaryotic organisms. All true algae have a nucleus within a membrane and chloroplasts inside one or more membranes. However, algae are definitely "not" a monophyletic group, as they do not all descend from a common algal ancestor. Modern taxonomists propose splitting them up into monophyletic groups, but not everyone agrees how to do this.