You can see this on the BBC Four Botany: A Blooming History for a clear picture when using with students. 

This video clip from the BBC (from the TV series Botany: A Blooming History) introduces 18th century botanist and entrepreneur Thomas Fairchild and his pioneering work into speciation.

Thomas Fairchild was the first to artificially cross two plant species and produce a 'new' plant, a hybrid between a sweet william and a carnation pink. Darwin's ideas about natural selection and evolution of plants are discussed and the divergence of species represented by the 'tree of life' is explained. This is then used to explain why the hybrid produced by Thomas Fairchild was sterile - the original plants being of different species.

Use in lessons covering evolution and speciation or as an example of artificial manipulation of life. Could contribute to discussions of genetic modification.