The Journal of Horticulture says:

"An American writer wishes that 'the name Chrysanthemum could be shortened, as it causes some trouble to those who are not familiar with botanical names. We hear them called Cassan-thiums, Chrysantheums, as well as Chrysantum-bums, Chrysants and Chryschianthems.' To these might be added a daring abbreviation in common use amongst English growers - namely, 'the Mums.' "

As they are jovial flowers about Christmas time, some American ladies call them Christmas Anthems.