Bulbasaur appears to be based primarily on some form of reptile or synapsid, specifically mammal-like synapsids known as Dicynodonts from the Permian period. Along with visible ears and no genuine metamorphosis stage (evolution aside), Bulbasaur appears to have more in common with mammals than amphibians such as frogs and toads, which metamorphose from one definite creature into another as they mature as opposed to just growing into a larger adult version of itself the way that Bulbasaur does. Alternatively, Bulbasaur's large rounded snout, wide mouth, wide-set eyes, blotch-patterned skin, and quadruped-like movements are vaguely similar to those of certain amphibians, such as the common toad. Since Bulbasaur's "ears" do not in fact have hollows, they may actually be similar to the glands present behind the eyes of many species of frogs and toads.

The bulb on its back may resemble that of a lily or onion.