Legends say that Venusaur is like the guardian of the flora - its presence is enough to make flowers and plants to look more beautiful and healthier - but no studies have proven that yet. It is true, however, that Venusaur is responsible for pollination of most of the flowers in its natural habitat, because of the giant flower in his back.
Venusaurs don’t usually live in groups, unless in the pollination season (when Venusaurs need to gather so they can reproduce) or in the evolution season (when Bulbasaurs search for a Venusaur leader so they can evolve into Ivysaur). Research has shown that Venusaur’s pollen is very important to the growth of a Bulbasaur into Ivysaur, even if it isn’t indispensable (domesticated Bulbasaur can evolve without the help of a Venusaur).
It’s easy to know when a Venusaur is too old and in the end of its life; it’s when the giant flower starts to die. Nevertheless, a full-grown Venusaur can live hundreds and hundreds of years and is considered one of the most ancient pokémon from Kanto, with proof of his existence in pre-historical ages.