In the Victorian period, the language of flowers was a very real means of communication, and flower symbolism remains popular today. When I first read about the language, I remember thinking it sounded terribly romantic, and exactly the sort of thing Nasser would find interesting. Eventually, the language of flowers worked its way into the Flicker series.
Interestingly, the language of flowers wasn’t only used to express feelings of love. There was a flower to say just about anything : betrayal, grief, happiness, utter loathing, and so on.
The flower meanings I use in my books come from Language of Flowers by Kate Greenaway, which you can read for free online through Project Gutenberg.
There are many other online resources on flower symbolism, such as this one. Note, however, that every source is a little different. Today, there isn’t a single source with all the “real,” definitive flower meanings, just as there wasn’t one in the Victorian era.
Oh, and a fun fact: While four-leaf clover is known for its magical properties and as a good luck charm, in the language of flowers, it can also mean “be mine.”