What do they mean?

Every flower means something; on the base of this meaning the language of flowers was created. Every flower has its own symbol that sometimes changed during the development of human society.
Greek people considered aster to be the symbol of love. They were always associated with the goddess of love Aphrodite. This was also a goddess of beauty and gracefulness. The same meaning aster had in China. Aster means beauty, elegancy, charm and shyness in China. This flower is associated with autumn in Hungary. That is why this flower is called "autumn rosy". Besides, this flower is a symbol of Virgin in horoscope and it is a symbol of women in general.
Ancient Greeks considered delphinium to be the flower of sadness and grief. In Russia delphinium is considered to be a flower that has curing abilities.
Marigolds are considered to be the flowers of long life that is why they are called "flowers of thousand years". In India this flower was the incarnation of Krishna. In the language of flowers marigolds mean loyalty.
Iris was a symbol of courage in Japanese traditions. Maybe because of this the words "iris" and "courage" were marked by the same hieroglyph. There is a holiday named "The day of boys" in Japan. And this day every family that has a son put a lot of objects that have the image of iris. One of the most famous drinks is also made of iris. They believe that boys get courage taking this drink. This drink is also considered to have curing abilities.
But in Egypt this flowers was the symbol of oratory. It was also the symbol of sadness and grief in some countries of the East. That is why white iris was planted in cemeteries.
Rose is the flower that has a great number of symbols. But almost every country and nation considered it to be the symbol of love and passion. But is also considered to be "the queen of flowers" that is why it became the symbol of greatness and nobility. There are a lot of artworks where the rose is the symbol of grief and parting. In some cultures this flower is a symbol of luxury and richness. And sometimes it is even a symbol of danger.
Violets mean beauty and simplicity. It is universal symbol of friendship, optimism and dear relations between people. Violets were considered to have some curing abilities; they were put on the wound to heal it.
Flowers may tell us a lot. Symbols they have were created by every nation but sometimes a flower got its meaning thanks to artists and lovers. Flowers inspire and allow telling something you are not able to say using words.