Botanical names have the distinct advantage of referring to one and only one plant, with certain exceptions. The use of these names makes communication between widely scattered gardeners more precise. Now that the internet has made this planet as small as the street where you live, it is more important than ever to insure that we are both referring to the same plant if discussions are to have any meaning. If you point out a sunflower to a neighbor, there is understanding. Well, I just used a strange word.
Genera is the plural of genus, and genus is one of the components of a plant name.
The binomial system of naming all organisms on this earth groups them into various kingdoms, divisions, orders, families, and genera. So, the genus is the basic grouping of similarity or relationship between organisms. In Latin, it is a naming noun derived in part from medieval Latin, classical Latin, and latinized versions of words in other languages, principally Greek. Solanum , for example, is a Latin word for a group of plants which includes herbs, shrubs, trees, and vines. There are 1400 species in this group.