From Nookipedia, the Animal Crossing wiki
Flowers in the Animal Crossing series are small clusters of brightly colored flowers that live throughout all four seasons. They can be bought from Tom Nook's Store, are grown by villagers, and grow randomly around the town.
There are four common types of flowers: roses, cosmos, tulips, and pansies. Flowers wilt periodically, turning a brown color. They can be revived by being watered with a watering can on the same day that they wilt, and will return to normal the following day. This wilting process applies to all flowers but the golden rose, which is created after watering a black rose with a golden watering can.
In Animal Crossing, flowers cannot breed or wilt. All sorts of colors can be bought from Tom Nook without the need to hybridize. Also, they cannot be picked up like in later games, so they cannot be sold or worn.
Various combinations of flowers can be bred to form new colors, such as the yellow and red pansies, which create an orange pansy.
In City Folk, flowers play a major part in the restoration of damaged grass. Flowers can also be worn in a player's hair. A flower worn this way will take the place of a hat. In the case of a rose, however, it is held between the teeth and will take the place of an accessory or helmet.
In Template:AC3DS, flowers will grow in groups of four, rather than in threes. It is unknown if any new types of flower will appear.
Carnations can only be obtained in City Folk. There are three colors - pink is obtained from the player's mother on Mother's Day (May 10th), the red is obtained from the player's father on Father's Day (June 21st), and white is created as a hybrid of the two.
Clovers grow frequently and are generally treated as weeds, disappearing after being pulled. However, the four leafed-clover grows very infrequently and is placed in the player's inventory. It has been known to affect luck, and can be worn in the hair or placed as furniture in the player's house, used as a bookmark.
Dandelions appear randomly around the town, and are essentially classed as a weed, despite not affecting the town's environment. They look like a brighter version of a sun cosmos, with thinner, fuller petals and heavier leaves.
The dandelion puff can only be grown when a normal dandelion is left for a certain space of time. The dandelion puff is a collection of seeds with white parasols. This item, when held, can be blown by the player, hence the name "puff." When blown, the seeds float away and disappear into nothing. In City Folk, the parasols are much more realistic, complete with seeds.
When the environment of a town reaches perfect level, the Jacob's Ladder flower grows around the town. This flower does not have any variations, only appearing as a cluster of whitish-green buds dangling from a leafy plant. This plant does not breed when placed next to other Jacob's Ladders.
The rafflesia is a large red plant that grows in the player's town after a large number of weeds accumulate. Once this plant appears in town, it means that the town is at the lowest rank, not a perfect town, etc. In reality, the plant is notorious for its smell; which, in game, is reflected by the presence of flies. After the removal of the weeds, the rafflesia will wilt, then disappear. To rid the town of weeds, talk to Wisp the ghost and bring back all five spirits. Ridding the town of weeds is one of three choices as a reward. In many ways, it is the polar opposite of the Jacob's Ladder.
Hybrids can be obtained from Wild World onwards. In Animal Crossing, hybrids could be bought from Tom Nook's, but could not be bred.
How to Hybridize
If two different specimen of the same species are planted next to each other, on the next morning, there is a chance they will hybridize and create a new flower in one of the spaces next to either of the parents. For example, red tulips and white tulips can produce pink tulips. There are a few guidelines to follow to do this.
Even if the hybridization conditions are met, there is no guarantee it will occur. Only three to five new flowers appear in a town in a day, and most hybridization pairings can produce a non-hybrid child, so it may take a while for any particular hybridization to occur. There are a few things that are thought to increase the chance of hybridization.
Once a hybrid is produced, it can reproduce quickly by crossing it with any other flower. Just be aware not all flower can hybridize.