Cattail

The Cattail is the upgrade for the Lily Pad. It costs $10,000 to buy from Crazy Dave's Twiddydinkies and 225 sun to upgrade the Lily Pad in the Pool. Its tail and name are based on the Typha latifolia, the Cattail or reed, a perennial herbaceous plant in the genus Typha. Its face, however, is based on the domestic cat. It fires spikes to any lane at a speed twice the speed of a Peashooter or at speed of a Repeater. It is available for purchase after Level 4-4.

Suburban Almanac Entry
Cattail 

Cattails can attack at any lane and shoot down balloon zombies too.

Must be planted on lily pads

"Woof!" says Cattail. "Woof woof woof! Does this confuse you? Do you expect me to say 'Meow' like a cat because the word 'cat' is in my name and I also look like a cat? That's not how things work around here. I refuse to be pigeonholed."

Cost: 225

Recharge: very slow

Usage
The Cattail has the damage and rate of fire of a Repeater. The Spikes it fires are homing, and can hit zombies anywhere. It attacks zombies closest to the plant, though it prioritizes Balloon Zombies. However, they can only attack a few Shield Zombies around their Shields. It is very useful for killing Digger Zombies if they're in the back row, as it will kill them before they can even move.

Strategy
Because a single Cattail can cover all six lanes, it makes a good early defensive plant. It also helps deal with Digger Zombies, Imps, and Balloon Zombies. However, they are easily overran because of the ability to cover all six lanes, as Cattail may be targeting a Conehead Zombie, then a Pole Vaulting Zombie that is closer to the Cattail draws its fire, letting the Conehead Zombie go on unattacked. Also, all your Cattails will usually fire at the same target (except under certain conditions), and when that target dies, spikes in the air are wasted. This limits the effectiveness of large numbers of Cattails. It is a good idea to use Cattails in limited numbers in Survival levels that take place in Pool or Fog. Also, do not rely on Cattails for pool defense, since they will be inevitably overwhelmed. When playing a Survival: Pool Hard level, you want to get Cattails, but back them up with more consistent firing plants such as Repeaters or Melon-pults in the Pool.

Trivia

 * The Cattail is the only aquatic plant that is an upgrade.
 * It's also the only offensive Upgrade Plant that upgrades from an unoffensive plant.
 * Cattail, Gloom-shroom, Split Pea, and Starfruit are the only plants who can shoot backwards. However, Cattail can attack any lane. Gloom-shroom can only attack 1 block near, Split Pea and Starfruit can't attack other lanes backwards.
 * The Cattail does the damage of a pea and rate of fire like a Repeater, making it an aquatic version of a Repeater.
 * However, its shots are homing, so it's much better. On the other hand, they cost 50 more sun (25 for the Lily Pad and 25 extra sun for the Cattail), and Cattails can get even more expensive in Survival: Endless.
 * A Cattail can be downgraded to a Lily Pad if you have a Pumpkin on it and try to dig up the Cattail, as that would cause the Pumpkin to fall into the water otherwise.
 * Bungee Zombies can also downgrade a Cattail with a Pumpkin.
 * The Cattail is the most expensive aquatic plant, costing 225 (25 extra for Lily Pad) Sun with a 250 sun total.
 * However, this value can rise in Survival: Endless due to the increasing price of upgrade plants.
 * During the ending credits of Zombies on Your Lawn, it is shown next to Laura Shigihara's name.
 * According to this website, this is because Cattail is her cameo plant, because she wears a hat similar to Cattail's when it's cold.
 * When a zombie is defeated and the spikes from Cattails are still aiming for the same direction, it will not damage the Zombie behind the defeated one (unlike some other projectiles, which hit the zombies at the back).
 * This may be due to the fact that Spikes are "homed in" on the zombie the Cattail aims for.
 * The Cattail is a pun upon the Typha latifolia, commonly known as a cattail, as evidenced by the Cattail's cat's head and its tail having a Cattail seed structure.
 * The Cattail's spike moves slower than the Cactus's.
 * The Cattail, the Starfruit, the Gloom-shroom, the Cob Cannon, the Cherry Bomb, the Winter Melon or Melon-pult (splash damage), the Doom-shroom, and the Threepeater are the only plants that can hit zombies in other lanes.
 * Cattail seems to be standing on a folded Lily Pad, or maybe has four Lily Pads for "legs".
 * The Cattail and the Lily Pad are the only aquatic plants that can have a Pumpkin on them.
 * The Cattail is one of the two plants with a tail, the other one being the Cob Cannon.
 * The Cattail, the Cactus, and the Sea-shroom are the only projectile-shooting plants that use a projectile that is colored significantly differently from the plant itself.
 * The Cattail's spikes on the DS version of the game will sometimes miss the zombies, and keep circling it until it dies.
 * Also, sometimes in the DS version, the spikes will not target zombies, but fly straight ahead and rotate slowly.
 * The Cattail has the longest range among the shooting plants.
 * The Cattail, the Imitater, and the Gatling Pea are the only plants with headwear.
 * If you look closely, the Cattail has one tooth sticking out, similar to the Starfruit and Potato Mine, but the Cattail's is a fang.
 * Cattail can fire in the most directions. The plant that fires in the second most directions is Gloom-shroom (eight) and the third is Starfruit (five).
 * The Cob Cannon can also hit the zombies in all directions.
 * Cattail is one of four plants who can fire at a Digger Zombie, the others being Gloom-shroom, Split Pea, and Starfruit.
 * Cattail is also one of three plants who can get rid of Balloon Zombies. The others are Blover and Cactus.
 * In Plants vs. Zombies 2: It's About Time, the Snapdragon resembles a dragon, so this is the only plant in Plants vs. Zombies  to resemble an animal.
 * Surprisingly, Cattail will not aim at a Snorkel Zombie. This is odd because it can fire anywhere on the screen and will aim at Balloon Zombies.
 * This is possibly because it can't see it. It may also be because it can't fire at it as the Cattail might not be able to fire heights that low.
 * The Cattail, Marigold, and Starfruit are the only plants with one tooth.
 * Cattail-pole_vaulting.png a Cattail is targeting a Pole Vaulting Zombie and the zombie vaults, the Spikes will act as it would if the zombie already died, but when the Pole Vaulting Zombie lands, the spike will turn around and attack the zombie again.
 * The Cattail, Lily Pad, Tangle Kelp, and the Sea-shroom are the only aquatic plants that have a splashing sound when planted.
 * Although this may be due to the low number of aquatic plants.
 * In the Mini-game Heavy Weapon, the Cattail's tail is pink instead of brown.
 * Cattail bears a slight resemblance to the Pokémon Skitty.
 * Coincidentally, Cattail is female, and Skitty is often referred to as female.
 * It is strange how the Cattail can support a Pumpkin, as the Pumpkin looks like it is floating.
 * The Cattail and the Cactus are the only plants to shoot spikes.
 * The Cattail doesn't act like a cat despite its look; it behaves more like a dog since it barks (as its Suburban Almanac entry states).
 * You cannot plant a Cattail on a Lily Pad with a plant besides a Pumpkin on it.
 * If Cattail is planted in the very front rows, its spike cannot home into zombies.
 * The Cattail will not attack unless there are zombies in the 2nd lane or farther.
 * The Cattail may be based on Hello Kitty.
 * The Cattail only has a tongue as a plush toy.
 * Cattail is the only upgrade plant that must be planted in water.
 * Cattail is the plant preferred by Laura Shigihara.
 * Cattail is the one of two plants in the game with a nose, the other being Pumpkin.
 * In some versions, when a Zombie targeted by a Cattail is not killed by the Cattail, the spikes fired targeting the dead zombie may circle around the dead zombie's death location. This behavior has been seen in the most recent Android update.