Cattail

Cattail is the upgrade for the Lily Pad which costs $10,000 to buy from Crazy Dave's Twiddydinkies and 225 sun to upgrade the Lily Pad in the Pool. It fires spikes at any lane at the speed of a Repeater. It is available for purchase before playing Level 4-5.

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.

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

Plant Food upgrade (Plants vs. Zombies: All Stars)
Perceive weakness: Shoot 3 spikes to the enemy with lowest health. It requires Brave Plant Food to be activated.

Usage
Cattail has the damage and rate of fire of a Repeater. The spikes it fires home in on zombies and can damage zombies regardless of their position on the lawn. It attacks the zombies closest to the plant, although 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 are in the back row, as it will kill them before they can even move.

Strategies
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 a 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, so it is recommended that you don't rely solely on Cattails for pool defense.

It is a good idea to use Cattails in limited numbers in Survival Mode that take place in Pool or Fog. Do not forget to back them up with more consistent firing plants, such as Repeaters or Melon-pults.

Specific to Plants vs. Zombies

 * Cattail is the only aquatic plant that is an upgrade and is also the only offensive upgrade plant that upgrades from an unoffensive plant. It is also the only aquatic plant that needs to be planted on Lily Pad.
 * 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 one block near it, while Split Pea and Starfruit cannot attack other lanes backwards.
 * 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. 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 the player has 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. This makes the Cattail the only plant able to downgrade.
 * 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.
 * When a zombie is defeated, 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).
 * Cattail is a pun upon the Typha latifolia, commonly known as a cattail, as evidenced by Cattail's cat's head and its tail having a Cattail seed structure.
 * Cattail's spikes moves slower than Cactus's.
 * Cattail, Starfruit, Gloom-shroom, Cob Cannon, Cherry Bomb, Winter Melon or Melon-pult (splash damage), Doom-shroom, and Threepeater are the only plants that can hit zombies in other lanes.
 * Cattail and Lily Pad are the only aquatic plants that can have a Pumpkin on them.
 * Cattail is one of the two plants with a tail, the other one being the Cob Cannon.
 * Cattail, Cactus, and Sea-shroom are the only projectile-shooting plants that use a projectile that is colored significantly differently from the plant itself.
 * Cattail's spikes on the Nintendo DS version of the game will sometimes miss the zombies, and keep circling it until it dies, as well as not target zombies, but rather fly straight ahead and rotate slowly.
 * Cattail has the longest range among the shooting plants.
 * Cattail, Imitater, and Gatling Pea are the only plants with headwear.
 * If one looks closely, Cattail has one tooth sticking out, similar to Starfruit and Potato Mine, but 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).
 * Cattail is one of four plants which 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. However, Cattail is not listed as a weakness of Balloon Zombies in the Suburban Almanac entry.
 * 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 cannot see it. It may also be because it cannot fire at it as the Cattail might not be able to fire heights that low.
 * Cattail, Marigold, and Starfruit are the only plants with one tooth.
 * When 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.
 * This also happens when a Balloon Zombie loses its balloon or when a Dolphin Rider Zombie loses its dolphin.
 * It is the fourth and last aquatic plant that can be unlocked.
 * In the mini-game Heavy Weapon, the Cattail's tail is pink instead of brown.
 * It is strange how the Cattail can support a Pumpkin, as the Pumpkin looks like it is floating.
 * The player 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.
 * Cattail will not attack unless there are zombies in the second column or farther.
 * Cattail only has a tongue as a plush toy.
 * Cattail is the only upgrade plant that can be planted only in water.
 * Cattail is the one of two plants in the game with a nose, the other being Pumpkin. However, Pumpkin's nose is just a hole, but Cattail's nose is real.
 * In some versions, when a zombie targeted by a Cattail is not killed by it, 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.
 * It has a counterpart in Plants vs. Zombies 2, which is the Homing Thistle.
 * The Cattail seems to act like a normal plant on a Lily Pad, as they cannot plant anymore plants on the cattail and it can support a Pumpkin.

Specific to Plants vs. Zombies: All Stars

 * Cattail's, Dogtail's, and Liontail's elements are Earth, but they use the slingshot (element for water) as their weapon.
 * Its spikes don't home in on zombies in this game. Also, it only shoots one spike at a time.
 * It can only be planted on land in this game.