As confusing as they seem to be, Latin names of plants are actually intended to simplify things. They work because they are universal, everywhere and in all languages. Common names may seem simpler, but are too variable in different regions and in different languages.
For example, the white pine that is native to Northern California is not the same as the white pine of Maine. However, only the white pine of California is Pinus monticola. Furthermore, it is known as Pinus monticola everywhere and in every language, even though it has different common names in French, Afrikaans and Vietnamese.
The first name of a Latin name, which should be capitalized, is the more general ‘genus’ name. (‘Genera’ is plural, and not coincidentally similar to the word ‘general’.) Pinus is the same genus name for all pines. Acer is the same genus name for all maples. Quercus is the same genus name for all oaks; and so on.
The second name of a Latin name is the more specific ‘species’ name. (‘Specie’ is plural, and not coincidentally similar to the word ‘specific’.) Monticola specifies the genus of Pinus as Pinus monticola, the white pine of Northern California. Radiata specifies another genus of Pinus as Pinus radiata, the Monterey pine; and so on. The species name is not capitalized. Technically, Latin names, both genera and specie, should be italicized in print or underlined in cursive.
Latin names work like the names of cars. Buick, Chrysler and Mercury are all like genera. Electra, Imperial and Grand Marquis are all like specie, or the specific Buicks, Chryslers and Mercurys. ‘Limited’, ‘Custom’ and ‘Brougham’ are like variety names, like ‘Variegata’, ‘Compacta’, and ‘Schwedleri’. For plants, variety names are capitalized and enclosed in semi-quotes.
As universal as Latin names should be, a few sometimes get changed. This can be confusing, and causes some plants to become known more commonly by either the new or old name as well as the other of the two names as a ‘synonym’. For example, Dietes bicolor and Morea bicolor are the same plant; but not many know for certain which name is more correct. It is like when Datsun became Nissan, but was also known as Datsun for many years afterward.
Tony Tomeo 
Name changes are confusing, nevertheless, I believe we should all use the correct nomenclature when talking about plants. Garden blogging is international and this is the only way we can possibly know what we are all talking about. I am often confused by American plant names in particular. Besides, if we take the trouble to learn a little Latin, there is often a clue as to which habitat would suit the plant best.
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Variation of common names is not just international. It is regional on smaller scales, such as between Northern California and Southern California, and even within various horticultural industries. Landscape designers use a few common names that are different from those that arborists use.
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I absolutely love this comparison of plant names to car names. It makes things so simple and easy to understand–especially the part at the end about when plants change names! Really great!
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Thank you. It always seemed like a practical comparison to me. I described it when working with arborists many years ago. They were familiar with cars (back when cars were worthy of such familiarity), but had difficulty learning the names of trees.
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I totally forgot about Datsun. I think one of the reasons I did not study horticulture was that I was scared I could not learn and remember all the Latin names.
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We tend to remember those that we work with most often. Cultivars and varieties are more complicated nowadays.
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Good analogy. Fortunately the nurseries I buy from still use the old names for most of the things that have been changed in recent years. Otherwise I might be a bit lost…. 😉
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Well, years ago, we were able to identify cars.
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😆
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