In Guardians of the Galaxy, The Collector implies that Groot is his own species (he says something like: "I have never met a Groot before") but as far as I can tell there is no evidence for Groot being a recognized Marvel race outside of the GOTG film.
Is it possible that Groot is of the H'ylthri species?
H'ylthri are an other-dimensional, sentient plant race. Their bodies are vegetable fiber with few vital organs, making them difficult to injure. They possess superhuman strength to an unspecified level, can control other plant life, and extend both tangling vines or poisonous barbs to knock mammals unconscious. They can grow humanoid doppelgangers with the originals' personality and memories
Or is Groot one of a kind like Rocket?
And if so how did The Collector recognize him?