Roselia is a small Pokémon with a light green body. Roselia has a leaf skirt and holds a rose on each of its hands, a red one in its right and a blue one in its left. Roselia has leaves extending from its shoulders like epaulettes, and a pointed streak of yellow extends from its neck down the forefront of its leaf skirt. Visible from the back is a small stretch of yellow coloration around its neck much like a collar. Roselia also has three thorns on top of its head.
A male Roselia has a shorter skirt than a female.
Roselia normally fire sharp thorns (either Poison Sting, Toxic Spikes or Pin Missile, but the latter of the three rarely occurs) as a first offense, usually at wild Pokémon who try to steal its flowers. Roselia are also capable of launching some Powder-based moves to either inflict status problems on its foes (Sleep Powder, Stun Spore, or Sweet Scent) or to heal the status problems of itself and its allies (Aromatherapy). Roselia are also capable of knowing Petal Dance. Like most Grass-type Pokémon, Roselia can take in sunlight and focus it into a SolarBeam.
Roselia seem to be peaceful Pokémon, but can attack fiercely with powerful poisonous attacks upon sensing danger.
Roselia was at one time the only dual-type Grass/Poison Pokémon that did not evolve into or from anything (though this changed when Budew and Roserade were introduced). It was also the only Pokémon with its specific type combination to not be from Generation I until its evolution and pre-evolution appeared.