Le Langage des Fleurs - Charlotte de La Tour
La Langage Des Fleurs is amongst the earliest of the 19th century language of flowers books, having been first published around 1819. While not the first book to cover the subject in Europe, it was the first completely devoted to floriography and was translated and published widely; and while not without modification, de La Tour’s system can be seen as the basis for the floriography systems that became popular in Britain.
De La Tour also cites Lady Mary Wortley Montagu’s 18th century letters from Constantinople - which describe messages sent through a variety of symbolic objects, perhaps as a means to pass messages in the sultan’s harem - to give an origin of the language of flowers in Turkey. Modern scholarship (and even some from the time) has shown that a more European origin is likely (likely in romantic bouquets in France), and in any event the Turkish system described uses many other objects besides flowers to derive its symbology.