The reason for that is simple, and rather practical.
Scientific names by and large are standard for any one particular species (with the minor point that names can sometimes change over time as the taxonomic placement of the species changes due to new information being uncovered).
Common names, on the other hand, can vary from one country to another, and many times even within one country! This dilutes clarity and introduces the chance for errors in identification. For example, in a single youtube search for videos I found that Arundo donax can be called a multitude of names, including Giant Reed Grass, Arundo Cane, California Bagpipe Cane, Tube Cane, and Giant Cane.
In addition to dispelling confusion about a plant when communicating, the use of scientific nomenclature also has another advantage. It automatically allows people to group similar plants together. This is because a scientific name has two parts to it: The genus name (which is always capitalized), and the specific epithet (which is always in lower case).
In the same way, our own species is Homo sapiens, with Homo being the genus name (meaning 'human being') and sapiens being the specific epithet (meaning 'wise, intelligent'). One of our cousins in the human lineage is Homo erectus, a species related to us from 2 million years ago.
|Poa bulbosa spikelets|