May's Venusaur was May's first Kanto starter Pokemon which she caught in Hoenn
Venusaur was caught as a little Bulbasaur which lived with many grass Pokémon on a special territory. As May ends up in the forbidden area she is chased by the grass Pokémon, but is saved by the little Bulbasaur who eventually joins her team when May is about to leave. Bulbasaur came as a big help to her team with the learned move Petal Dance which was used with a lot of elegance. Bulbasaur acknowledged Ash's Bulbasaur as the two are good friends. May makes a comeback in Sinnoh saga revealing her new Pokémon as well that she evolved her Bulbasaur twice during her journey in Johto. Venusaur's current attacks are unknown than only Vine Whip and those Bulbasaur once knew.
May's Bulbasaur is most likely female due its introduction in the episode it first appeared, it was plucking flowers. When it evolves into Venusaur, it is proven that it is female because it has a seed in the plant on its back.