The plant that shoots peas down three lanes at once is Threepeater.
Threepeater is an offensive plant in the original Plants vs. Zombies, firing one green pea straight ahead and one pea into each adjacent lane. That lets a single plant cover three horizontal rows, making it especially useful when zombies are approaching in neighboring lanes.
It is often confused with Repeater, which fires two peas down only one lane, or Gatling Pea, an upgrade that fires four peas down one lane. Peashooter is the basic single-shot plant and does not spread its attack across rows. Threepeater’s multi-lane attack also explains its name: “three” refers to the three lanes it can cover.
The original game’s lawn normally has five lanes, although pool stages expand the battlefield to six lanes. Threepeater remains useful in either setting because it attacks the lane where it is planted plus the two lanes beside it, though players must position it carefully near the edges.