This Cacnea is a Grass-type Pokémon previously owned by James. It was the first Pokémon he caught in the Hoenn region. Eventually, James gave Cacnea to Gardenia for training.
Every time Cacnea came out of its Poké Ball to battle, it would latch onto James out of affection, which would hurt him with its spikes. It met him and is crew right before James released his Weezing, and it saved them from a group of Beedrill. Cacnea was still following them to open the box James had given to it. Not that long after Weezing's release, Cacnea joined James' Team. Later when Jessie and James were in Sinnoh after their travels throughout Hoenn and the Battle Frontier, James decided to leave Cacnea with Gardenia to master its Drain Punch move.
Cacnea was James' first Pokémon caught in the Hoenn region.
Cacnea has some similarities with Ash's Bayleef. They are both Grass-Types, they both insist on hugging their trainers after being sent into battle, both cause problems when this happens, and both made an appearance in the Sinnoh region.