From Bulbapedia, the community-driven Pokémon encyclopedia.
The Gracidea (Japanese: グラシデアの花 Gracidea Flower) is a key item introduced in Pokémon Platinum that changes Shaymin between its Land and Sky Formes. The flower is native to Gracidea, hence its name.
In the games
The flower can be received in Pokémon Platinum during the player's first or subsequent trips to Floaroma Town, although the player's party must contain a Shaymin received from a Nintendo event or one caught by the player by unlocking Oak's Letter via Mystery Gift. This item cannot be used at night or when Shaymin is frozen. In some places people give bouquets of these flowers that resemble Shaymin, as seen on the right, to thank someone. This comes from Shaymin's species, Gratitude.
In Pokémon HeartGold and SoulSilver, the Gracidea flower is obtained in the Goldenrod City flower shop. The same conditions must be met as in Platinum, and Shaymin must also be at the front of the party (i.e. following the player).
In Pokémon Black and White, if a fateful encounter Shaymin is shown to a woman in Lacunosa Town's Pokémon Center they will get the Gracidea flower.
In Pokémon Black 2 and White 2, the Gracidea flower is obtained from a woman in Striaton City's Pokémon Center. The same conditions must be met as in Black and White.
In the side games
The Gracidea appears as a toy in the Japanese version of My Pokémon Ranch, after receiving the Platinum update. As in the handhelds, it is used to change Shaymin between its Land and Sky Formes. It only appears if the player has the Gracidea on their Platinum cart. As this update is unavailable outside of Japan, the Gracidea cannot be obtained outside of Japan as well.
In spin-off games
In the Pokémon Mystery Dungeon series
In Pokémon Mystery Dungeon: Explorers of Sky, a Gracidea can be obtained once per day from one of the citizens of Shaymin Village after the player recruits one of them. The flower can only be used in a dungeon, and upon leaving the dungeon, Shaymin reverts back to the Land Forme. A bow resembling a Gracidea flower also appears on the Sky Gifts found in Sky Peak.
In the Pokémon Ranger series
A field of Gracideas is found in Latolato Trail in Pokémon Ranger: Guardian Signs. In a Special Mission involving Shaymin, the flowers in the field is used by Shaymin to transform.
In the PokéPark series
In PokéPark Wii: Pikachu's Adventure, Gracideas appear in the Flower Zone. It is necessary to water these Gracideas to make them bloom. Shaymin will then change form and guide the player to the Sky Pavilion.
In the anime
In the movie Giratina and the Sky Warrior, a character named Layla owns a Gracidea bouquet, which has the same purpose as it does in Platinum. Shaymin also live in a field full of these flowers.
In Strategy Begins at Home!, Johanna's garden had flowers that look similar to Gracideas.
Gracideas appeared again in Keeping in Top Forme!.