Belldew sprout vines to take care of the bulb atop their heads by keeping it clear of debris. When an herbivorous Pokémon tries to eat them, they sprout razor sharp leaves that cut at the face of the herbivore.
Over the winter, it closes its bud and endures the cold. A Belldew's thin and flexible body lets it bend and sway to avoid any attack, however strong it may be.