What flower means prosperity?

There doesn't appear to be any specific flower that carries this distinction. To quote from a page on the the AboutFlowers website (http://www.aboutflowers.com/floral_b5.html);

In Victorian times, certain flowers had specific meanings because the flower selection was limited and people used more symbols and gestures to communicate than Words. But today, with so many flower choices, there are no rules - it's the sentiment that gives the gift its meaning. Many people assign their own personal meanings - a flower or color that might remind them of a special event or moment in their lives.