This Treecko is a grass-type Pokémon owned by Stephanie's father.
Stephanie's father's Treecko was being watched by Nurse Joy, along with Stephanie's soon to be Mudkip and a very tough Torchic. While Ash and his friends were at the Pokémon Center Nurse Joy complimented on how well their Treecko, Torchic and Mudkip were raised. She asked them if they could watch the younger ones as Max let them out of their Poké balls.
None of Treecko's moves are known.