Cactus

The Cactus is the primary anti-air Plant. According to its Suburban Almanac entry, it is female.

The Cactus could be any member of the genus Cactaceae, but it most resembles a Saguaro Cactus, but with a red flower instead of a white one.

Usage
The Cactus is essentially a Peashooter that shoots spikes, although it can stretch into the air to pop Balloon Zombies' balloons.

Suburban Almanac Entry
Cactus

Cactus shoot spikes that can hit both ground and air targets.

Damage: normal

Range: ground and air

She's prickly, sure, but Cactus's spikes belie a spongy heart filled with love and goodwill. She just wants to hug and be hugged. Most folks can't hang with that, but Cactus doesn't mind. She's been seeing an armadillo for a while and it really seems to be working out.

Cost: 125

Recharge: fast

Strategy
Build a column of them to keep your lawn safe from Balloon Zombies. They also make a good substitute for the Peashooter on any level you might encounter Balloon Zombies, although even though the cost difference is negligible, there is a disadvantage that if even a single Balloon Zombie comes into the lane, all of the Cacti will rise and fire at it. If there are no Balloon Zombies, however, you may be better off with peashooters. It is cheaper in pool levels to use 2 Cattails instead of six Cactus.

Trivia

 * The Cactus is referred to as a female in the Suburban Almanac, making it the only female plant in the game besides the Marigold, Sunflower, the Hypno-shroom, the Umbrella Leaf and Twin Sunflower.
 * The Cactus is one of the 3 plants that can get rid of the Balloon Zombie. The two others are the Cattail and the Blover.
 * Even if the Cactus and the Cattail have the same projectile, the Cactus' projectile is faster that the Cattail's.
 * If stretching, the Cactus has the size of a Tall-nut.
 * The Cactus, the Cattail, and the Sea-shroom are the only projectile-shooting plants having a projectile which has a color not similar to the plant's color.
 * The Cactus cannot work on the slope (except for the 5th row) on Roof levels. This is awkward because the Cactus is supposed to stretch taller.
 * Cactus is one of the twelve plants that appear in the seed selection screen after you get the Grave Buster on the online version, the others are: Ice-shroom, Lily Pad, Potato Mine, Threepeater, Tangle Kelp, Jalapeno, Spikeweed, Torchwood, Tall-nut, Doom-shroom and Blover.