Popcap knew the original Plants vs. Zombies was going to be a hit as it took forever to be released on many platforms. While not a licensed version, independent developers have created a version for the Sega Genesis, a platform that was probably WAY down the list of soon to be supported platforms.
There are a few things that will be noticed right off the bat by most avid PvZ fans. For one, the Genesis version is missing frames of animation, particularly in the pea shooters. This is understandable as this is an unlicensed game and probably just a “can we do it” release. For PvZ fans that have to play/download every version you can add this one to your collection by downloading it here.