Flora colossus, commonly referred as Groot, are a species of plant-like organisms native to the planet X. The most noteworthy individual from this species is a member of the Guardians of the Galaxy.
One of the Flora colossus, Groot, became involved with the criminal Rocket, becoming a friend to him as well as Rocket's partner in crime. Groot fought in the Battle of Xandar and became a member of the Guardians of the Galaxy.
Few individuals in the known universe speak "Groot": Rocket Raccoon is well versed in it, and later the other Guardians of the Galaxy seem to have picked it up, as shown when they scolded Baby and Adolescent Groot for his foul language. Thor also knows the language, which allowed him to converse with Groot during his journey to Nidavellir.
The language is simply the phrase "I am Groot"; however, "we are Groot" can also be used in rare occasions. The language seems to be tonal and is incomprehensible to the untrained ear. It seems to be based on intonation, where "I am Groot" can mean many things.
Flora colossus are humanoid in form with a thick, robust body structure that makes them almost invulnerable to physical harm.
They have a highly-accelerated healing factor, able to regrow limbs and even their entire bodies from nothing more than a twig.
They have complete control over their bodies, able to extend their limbs as vines to reach high places or as whip-like weapons, grow twigs on any part of their body as a threat display or shield, change their body shape, grow leaves or flowers, and release bioluminescent airborne seeds.