Super Mario Kart
These Piranha Plants first appeared in super mario kart in the course Choco Island 1 and 2. There are scattered around the track and even some in the mud. They snap their petals and don't move around.
Mario Kart 64
These Piranha Plants in Mario Kart 64 appear biting up and pull over if the player hits one. They are on the edges of the track in Mario Raceway.
Mario Kart: Double Dash!!
Piranha Plants then appear in Mario Kart: Double Dash!! Mario Circuit, where there are a few of them on each side when turning a U turn, and they will bite you if you are too close to them. They also appear at the very end of the course. They acutally snap out at you, blocking your path. They also appear in Yoshi Circuit at more points, and are harder to avoid. Fake metal piranha plants appear in Waluigi Stadium.
Mario Kart DS
They appear in Mario Circuit in this game as well! They appear in pipes (as in Mario Kart: Double Dash!!) and on the ground (as in Mario Kart 64). There are two that actually breath fireballs at you.
Mario Kart Wii
Piranha Plants appear in several courses here. The large Kart Piranha Prowler is based off of them.
Mario Kart 7
They appear in the New Course Piranha Plant Slide and for the first time they have their own course.
Mario Kart 8
They reappear in 3DS Piranha Plant Slide, and also are now an obtainable item.
Falco Stadium
Fake statued plants appeared in Falco Stadium. They seem to be made of wood and come out of pipes that are on their side in the halfpipe.