It's a reference to the film "American Beauty." The film features roses in many of its scenes. -- Thanks, Viaggiatore. I researched it a little and found out that it is also the proper name of a type of rose. :)

There' s indeed a famous Oscar movie entitled <American Beauty>. But in fact, american beauty can also refer to a kind of flowers famous in America. Considering your sentence above, which concerns flowers, american beauty may better be perceived as a kind of flower. In Chinese, it may mean 紅薔薇。B:)