Physical Origins.Bulbasaur is an odd creature, in that it combines physical traits from mammals, reptiles, amphibians, and of course, plants. It's body shape appears to be similar to a four-legged mammal and/or prehistoric creature. It's facial features, such as it's large eyes, slitted nose, and large mouth are similar to those of amphibians such as frogs and toads.
It's skin does not appear to be slimy, like an amphibian's would be, instead appearing to be tough and dry with darker scale-like parts on it like reptiles. This roughness is more apparent in it's final evolutionary form, Venusaur. The plant bulb on it's back appears similar to that of a lily or an onion.
All of these traits combined form the strange physical appearance of Bulbasaur, which is probably another reason for the origin of it's Japanese name as seen in the section below. It is indeed strange, but in an adorable way, of course.
Name origins.Bulbasaur's original Japanese name is Fushigidane, which is a play on words that translates both to "isn't it strange?" and "mysterious bulb." This name is, of course, in reference to the odd bulb planted on the Bulbasaur's back.
The English name of Bulbasaur is slightly less clever, combining the words "bulb" (again referencing the physical trait of the bulb on it's back) and "saur" (either from the Ancient Greek word for lizard, or from the word dinosaur, playing off of Bulbasaur's semi-prehistoric appearance.)