In Australia, where I grew up, we gave them for gifts in May for Mother's Day because in the Southern hemisphere that is when they bloomed. Here, they decorate our gardens in the fall and our tables for Thanksgiving.
Originally Chrysanthemums hailed from China, and they became popular in Britain in the 1800's. The plant explorer Robert Fortune brought the small button-type and pompom mums from the Orient but later plant breeders broadened the range of sizes, colors and types and conformation of the petals. They also bred the plants to withstand colder winters.
Now there are blossoms with incurved, quilled and spoon-shaped petals, football-sized ones, spidery shapes, doubles, cushions and anemone versions, in every color except blue!
The modern hybrid mums are classified based on their shapes and the arrangement of their petals. They seem to be everywhere-in grocery stores as well as florist shops, at all times of the year. They are airfreighted world-wide, as they are such serviceable flowers, easy to arrange and long-lasting in a vase.
They are also relatively inexpensive so make excellent hostess gifts for the holidays. If you are pressed for time as you prepare for Thanksgiving, buy three large mums, cut off the stems and float each one in a wine glass on your dinner table.