Before they were even known as the Guardians of the Galaxy, Peter Quill's rag-tag team of misfits were leading the charge against some of the biggest threats of the cosmos. Over the past few months, however, this has come in the form of one of their own, as Groot was transformed into the cosmic wave of destruction known as Grootfall. The Guardians initially opposed their teammate's new form until they were actually made into a part of him.
Source：https://www.cbr.com/guardians-of-the-galaxy-groot-origin/
