Puff-Shroom

Not to be confused with Puff the Magic Dragon 

Puff-shroom is the first plant you can get at night. You can complete all the one-flag levels, as well as 2-2, of the night levels just by spamming them all over the lawn. Although they can only shoot three squares in front of them, they are free and hence useful in starting a night level.

Strategy
Use these when there are only single Zombies. A conehead needs three to be reliably killed. They still have some use in the day without Coffee Bean, as miniature free Wall-nuts that take 6 bites. In ZomBotany, they can only be shot by a pea if they are on a Flower Pot.

Almanac
http://plantsvszombies.wikia.com/wiki/Puff-shroom#Suburban_Almanac_Entry

Trivia

 * It is the first night plant you get.
 * Two of them can just about defeat a slow Conehead.
 * It costs no sun, just like the Sea-shroom.
 * It is the first mushroom you get.
 * Its spores cannot go on fire.