i was wondering about the chlorophyllous green algae..

[oReNsama]

what is the probable ancestor of these chlorophyllous algae? is it endosymbiosis? *confused*

[SU_reptile]

Well that question is very difficult to answer with 100% certainty.
As far as endosymbiosis is concerned, there are several facts that may indicate on that way of evolution. For example algae from division Glaucophyta have bodies that resemble blue-green algae (Cyanophyta) namely their strucure and photosynthetic dyes are very similar (or the same). What's more, they have remains of cell walls.