If you're in search of a specific plant you want to make sure you get the real thing. You could always ask for it by its common name, of course, and you might get what you're looking for, but you might not. Knowing the plant's genus and species would help you be sure.
That's because common names vary widely for the same plant, depending on where you live. On the other hand, the plant's Latin name is based on an internationally accepted system and doesn't change. That's why plants and all other living things are named according to their genus and species.
And many plants have more than just the genus and species names. There are also variety names, which usually are in Latin (or occasionally Greek), and cultivar names, which aren't in Latin or Greek. These names are just as important as genus and species if you're shopping for a specific plant:
Variety names are subspecies of a given plant. The terms subspecies and variety are often used interchangeably. A variety is a plant that is slightly different from the species in some minor but noticeable way and may some day become a species.
In catalogs or on plant tags, variety names follow the genus and species names and may be preceded by the letters ssp. indicating a subspecies; var. or simply v designates variety. Cornus florida is the Latin name for the common flowering dogwood. But Cornus florida ssp. urbiniana describes a flowering dogwood that has bluish leaves, pink petioles and unusually large flowers. Variety names are italicized (you may find them not italicized in catalogs).
A plant that's been selected for its incredible color, unusual shape or some other characteristic and can be successfully propagated may be given a cultivar name. These names are easy to recognize because they aren't italicized and are commonly wrapped in single quotations marks. The cultivar name for coral bark willow is: Salix alba var. vitellina 'Britzensis.'
So make sure you know a plant's complete Latin name before you order.