One flower which I am reminded of is the orchid and conjointly, the Orchidaceae family. I am surprised when discovering there is an abundance of species and genera, hence I would like to know the exact number. Moreover, what is the reason, is this a quality resulting from angiosperms?
The Plant List records 27,801 accepted species names in 899 genera within Orchidaceae. This estimate probably differs a bit between authorities. For example the Angiosperm Phylogeny website records 26,000 species in around 880 genera. Regardless it is I think the most speciose angiosperm family.
The explosive diversification of orchids, like the diversification of angiosperms, has been a big study point for evolutionary biologists. A lot of explanations center around the wide array of floral morphologies which you can find in the group, as well as (although not independently) the evolution of a whole range of pollination strategies. Other factors include evolving in a tropical environment and the evolution of CAM photosynthesis in the group. You can find more details in, for example Givnish et al. 2015