Prin was told about green moss from her mother and the other adult Kin. When Lief, Barda, and Jasmine were attacked by a Vraal, she scared it off by clogging its eyes and ears with the dead, purple moss. She also gathered living green moss to tend to the companion's injuries. 
Green moss has the ability to cauterize and mend minor wounds and burns within a day or two. When it dies, the moss turns purple and burns the skin on contact. Green moss can be used to heal the burns caused by purple moss.