Instead, the give item node is labeled with the flag 10,1. Player is given the flower, which sets 10,1 to 250. A box for which the player needs a certain key, a special item. If the player has the item, jump to a dialog node saying they open the chest and find a pretty flower inside that they can take. Player steps on space, but doesn't have the key.
White dot remains, and they can try again later.
Player steps on space, has the key. White dot remains, and they can try again later. Player gets flower, flag 10,2 is set to 250. If player comes back, dialog shows message that you open the box with your key, and here's a flower. Player hits 'take,' but gets no flower, since 10,2 has already been set.