Cinzia Bruschini sent me this lovely rustic wedding centerpiece which is easily DIYed.
All you need is sheets of birch bark, seasonal flowers (in this case they are buttercups and thlaspi green bell) and thin rope.
Put the birch cortex together sandwich-style and stick the flowers in between. Then tie everything together with the rope. Done!
If the flowers are fresh, they should last a day even without water. Do keep them in the shade as long as you can, though.