From the Super Mario Wiki
Ads keep the MarioWiki independent and free :)
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, and Yoshi's Woolly World.
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 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 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. Dizzy Dandies are subterranean enemies that at first glance look like flowers, but have a different expression on their faces.
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 Medals via the goal roulette.
Yoshi's Woolly World
Smiley Flowers reappear in 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 course is unlocked in that world. If all Smiley Flowers are collected from all other courses, a special course in a special world is unlocked, called Wonderful World of Wool. The Smiley Flower will give Yoshi a chance to play a Bonus Game for extra Beads.
Names in other languages