From the Super Mario Wiki
Smiley Flowers, also referred to as Special Flowers or simply Flowers, are plant items that appear in Super Mario World 2: Yoshi's Island, Yoshi's Island DS, Yoshi's New Island, Yoshi's Woolly World, Poochy & Yoshi's Woolly World, and Yoshi's Crafted World. Their role is comparable to Dragon Coins and Star Coins. There are also evil smirking versions known as Fooly Flowers that attempt to trick the Yoshi into coming near them, then roll into them.
Super Mario World 2: Yoshi's Island
In the first entry in the Yoshi's Island series of games, there are five flowers in each level, and netting all five earns the Yoshi an Extra Life and fifty points toward the completion score (10 points per flower). Getting all the flowers in each level is also necessary for the Yoshi to get a perfect score. Collecting at least one flower is also necessary to access a Bonus Challenge via the goal roulette, and the chance of playing a Bonus Challenge is increased by collecting more. Flowers appear as sleeping seeds if frozen or not collected at the end of a level.
Yoshi's Island DS
Flowers also appear in Yoshi's Island DS, functioning the same way as in the game's predecessor.
Yoshi's New Island
Flowers return in Yoshi's New Island, now known as "Smiley Flowers" but functioning the same way as in the game's predecessor. However, as there are no score features or Bonus Challenges in this title, collecting all five increases the chances of getting Egg Medals via the goal roulette.
Yoshi's Woolly World / Poochy & Yoshi's Woolly World
Smiley Flowers reappear in Yoshi's Woolly World and Poochy & Yoshi's Woolly World, acting the same as in previous games. However, collecting all five does not give players an extra life, since the Yoshis have infinite lives. If Yoshi manages to collect all Smiley Flowers from a world, an additional level is unlocked in that world. If all Smiley Flowers are collected from all other levels, a special level in a special world is unlocked, called Wonderful World of Wool. The Smiley Flower at the Goal Ring will give Yoshi a chance to play a Bonus Game for extra Beads.
Yoshi's Crafted World
Smiley Flowers return in Yoshi's Crafted World, and like in Yoshi's Woolly World, they do not grant extra lives since Yoshi has infinite lives. The player also earns additional Smiley Flowers in a level for collecting a set number of coins, collecting all Red Coins, getting full hearts, finding the Poochy Pups, finding them within a set time, and finding all of the souvenirs. Yoshi must also give Blockafellers certain amounts of Smiley Flowers to advance to certain levels. Unlike previous games, they do not give the player a chance to play a Bonus Game. Unlike previous games, there are varying amounts of Smiley Flowers per level (between 5 and 8).
Yoshi's Island: Super Mario Advance 3
Yoshi's Woolly World
Poochy & Yoshi's Woolly World
Yoshi's Crafted World
Names in other languages