This algea magnified x1000 was found in an Evernia prunastri lichen. Trebouxia sp is the main photobiont for evernaia and most other algal lichens.
Asterochloris algea is the primary photobiont algea for Cladonia sp lichens. I found this algea in a Cladonia, therefore it is probably Asterochloris sp.
Here it is at x2000 magnification.
In taxonomy, the Trebouxiophyceae are a class of green algae, in the division Chlorophyta.