Floriography
The practice of giving flowers set meanings, so that a bouquet can carry a message.
Also: language of flowers
Floriography is the language of flowers. The idea that flowers stand for feelings is old and widespread, but it became a craze in 19th-century Europe and America, when small dictionaries of flower meanings sold widely. An early and influential one was published in France in 1819 under the name Charlotte de Latour. The books did not always agree. Some meanings have lasted: red roses for love, forget-me-nots for remembrance, rosemary for memory, white lilies for mourning.