It is believed that land plants are the most closely related to green algae, more specifically, a group of green algae referred to as charophyceans. Not only do both land plants and green algae produce chlorophyll a and b, but other evidence suggests that there is a relationship as well. For instance, land plants have cell walls made of cellulose, and green algae have cell walls made of cellulose. Furthermore, land plants are multicellular, eukaryotic, photosynthetic autotrophs as are certain green algae.
The green algae and land plants form a monophyletic lineage (the chlorophytes) that contains both protistan and higher taxa. An important issue regarding the evolution of this green lineage that still remains in question is the identity of the green algal (i.e., flagellate) ancestor of land plants.
The green lineage is, however, only one example of photosynthetic taxa that have successfully colonized our planet.