Genus and species
Genera are then divided into species, the basic unit of plant classification. The second word in a plant’s scientific name provides us with this detail and is known as the specific epiphet, the first letter of which should be in lower case.
Genus name + specific epiphet = Plant name
So for example, the scientific name of English oak is written: Quercus + robur = Quercus robur
Once a genus has been mentioned in text it may be abbreviated to its initial letter when part of a species name unless confusable with another genus beginning with the same letter, so for example Q. robur .
Subspecies, Varieties and Forms