2 species have Overgrow as a hidden ability, 27 as a normal one

Effect, in PokéAPI's words

“Strengthens Grass moves to inflict 1.5× damage at 1/3 max HP or less.”

As a hidden ability

Species	Slot	Note
Pansage	Hidden
Simisage	Hidden

As a normal ability

Species	Slot	Note
Bulbasaur	Normal
Ivysaur	Normal
Venusaur	Normal
Chikorita	Normal
Bayleef	Normal
Meganium	Normal
Treecko	Normal
Grovyle	Normal
Sceptile	Normal
Turtwig	Normal
Grotle	Normal
Torterra	Normal
Snivy	Normal
Servine	Normal
Serperior	Normal
Chespin	Normal
Quilladin	Normal
Chesnaught	Normal
Rowlet	Normal
Dartrix	Normal
Decidueye	Normal
Grookey	Normal
Thwackey	Normal
Rillaboom	Normal
Sprigatito	Normal
Floragato	Normal
Meowscarada	Normal

Elsewhere in PokéAPI

3 more holders without a page here

Alternate forms and other species that PokéAPI lists with Overgrow.

Venusaur Gmax, Rillaboom Gmax, Decidueye Hisui