If you're new to the study of plants you may also be new to the classification of plants and animals. In that case, we thought this page could clarify.
Plants, like animals are divided into different taxonomic groups. The highest order of classification is the domain. The lowest order that we'll deal with is species, even though breeders worry about varieties and biogeographers with subspecies. The following is a good example of a classification of a buckthorn:
You may have thought a "buckthorn is a buckthorn," a phrase that is an allusion to the Shakespearean "a rose is a rose". But this isn't the case. There are many types of buckthorns across the united states. They are all in the genus Fragula. The species is Fragula alnus, otherwise known as glossy buckthorn, alder buckthorn or frangula. Notice how the genus and species is italicized and only the genus is capitolized. Also notice how the species name is a combination of the genus and species: Fragula alnus. This name could be written also as F. alnus if the genus was already mentioned such as in the following statement:
"There are many Fragula species that are found in the US. These include F. alnus, F. betulifolia, F sphaerosperma and F. xblumeri."
Also note the name Frangula ×blumeri which is actually ahybrid between F. betulifolia and F. californica. Even though many people think that plants can not breed between different species, it is not true. Plants in closely related genera will often hybridize.
Are you confused yet? I hope not. The names are really not that hard, there are just a few rules that you need to know.
A final note
Throughout this site we have grouped the plants into plant families. The names are based on my own study under the instruction of Dr. G.D. Carr from the University of Hawaii. Since then some plant families have changed and certain families have either had plants added or taken away from their group. We are doing our best to stay current.