I just unlocked the special flowers. They all cost 1600 dust. The names are Radiant Rose for Mary, Chibi Cherry for Sakaki, Sparkling Strawberry for Cleo, Exclusive Erosa for Raquel, Towering Trollius for Annabell, Bizarre Briar for Leilani, Vernal Vesper for Yasu and Diffident Daffodil for Eva.

Appears they give 10 days to complete 5(?) quest stages. First stage for Mary is using 1 rain forest incense, 1 single rose and to complete 1 daily task.