Tropical leaves, one to a vase, make long-lasting arrangements for a fraction of the cost of flowers. Try Monstera leaf, Ti leaf, and Bird leaf; $2 to $13 each, all readily available at florists. Vases: Modenature small vase, $95; medium vase, $140: By special order at Interieurs, 212-343-0800. White bud vase by Hysteria, $27, by special order at C.I.T.E., 212-431-7272.