Black Eye Susan ???

I was so pleased this morning to see my first Black eyed Suzie in Flower,proper name Thunbergia, it made me wonder why plants and flowers have a proper and a common name and how this name came about !!
Anyway here it is, After standing outside with the hosepipe last night and being helped by my neighbours grandson to water the garden and then his parents,today we have had some terriffic showers and storms so I needn't have bothered,!
Hope you all enjoy whats left of the weekend and I am sorry for not replying so frequently to all your comments i have been so busy !.......honest xxb