Or who comes up with tongue twisters like Parthenocissus quinquefolia - and why?
Well here's the story...
It's a whole different language!
The Latinized names that are always in italics (or underlined) are called scientific or botanical names. Botanical names become valid only when they are published according to very specific rules, with illustrations and technical descriptions of the plant, in a scientific journal, and available to scientific libraries. Such botanical names are standardized and agreed upon throughout the world.
Then Why do Botanical Names Get Changed?
If it turns out that a botanical name was mistakenly given to a plant that already had a botanical name, or if the same name was given to more than one plant, then a correction must be made. You can't have the same name for two different plants and you can't have two different names for one plant. The first name published is the accepted one (the Rule of Priority), and any other names that may have been used incorrectly are now called synonyms. But these synonyms are not interchangeable as are synonyms in regular English. These synonyms are "unavailable" names that cannot be used. We often list botanical synonyms because not everyone always knows when a plant's name has been corrected.
There aren't any Romans around to correct us, so pronounce botanical names as though they were words in your own language, as best you can, one syllable at a time:
The basic unit of classification - and the basic unit of all life - is the species. Members of a species can interbreed with each other but not with members of other species.
The botanical name of a species has two words. The first, always capitalized, is the genus (plural: genera) and the second word is called the specific epithet or the specific part of the name.
An Example: Persea americana
The common name for this species is avocado or alligator pear or aguacate or palta. Whereas common names can be confusing and different in different places and in different languages, each species has just one accepted botanical name.
An unspecified (or unknown) species in the genus Persea would be written as Persea sp. To indicate more than one species of Persea, you would write: Persea spp., with two p’s. Once the genus has been used in a paragraph, or is understood, it can be abbreviated: P. borbonia.
Indicating a Name's Author For additional precision technical publications usually include the author (often abbreviated) of the name: Myrica cerifera L.
L. is the abbreviation for Carolus Linnaeus, the Swedish naturalist who first invented the binomial system of nomenclature in 1753. Linnaeus described and named the North American shrub, Myrica cerifera, also known as wax myrtle or bayberry. Professor Linnaeus named thousands of species of plants and animals based on specimens that were sent to him from collectors all over the world.
Building a Plant Name
Here’s that tongue twister again:
Parthenocissus quinquefolia (L.) Planchon
The species is: Parthenocissus quinquefolia.
Some common names are: Virginia creeper, Woodbine, American ivy, five-fingered poison ivy, five-leaved ivy. The “L.” means that Linnaeus first described the species; the parentheses mean he had originally placed it in a different genus. (Jules Emile Planchon (1823-1888) later transferred Virginia creeper to the genus Parthenocissus.)
What were Linnaeus and Planchon thinking of?
Linnaeus came up with quinquefolia from the Latin "quinque" which means five and "folia" which means leaf, referring to the distinctive five leaflets of Virginia creeper. He originally placed this species in the grape genus, Vitis, because it is very similar to a grape vine.
Several years later, Planchon decided Virginia creeper was sufficiently distinct from grapes that it should be in a genus of its own. He coined the generic name “Parthenocissus” from the Greek "Partheno" for virgin and "cissus" which means vine. Apparently he translated the American name, “Virginia creeper”, into Greek, and then Latinized it.
Botanical names don't have to mean anything, but they sometimes do.
Some plants are named after a person: Hypericum edisonianum is an endangered shrub in central Florida that was named for Thomas Edison. Or a place: Cornus florida. Or a color: Acer rubrum (rubrum is Latin for red). Or a shape: Viburnum dentatum (dentatum means "toothed", like a saw blade).
Taxonomy, or systematics, is the science of classifying living things. Systematists organize species into a hierarchy of categories based on their genealogy, or family tree, and not necessarily their physical similarities. Related species are grouped into genera, genera into families, families into orders, and so on. The main taxonomic categories for the southern crabapple are:
Some taxonomists (heir splitters?) use additional categories between these.
This brings us to the third (and last!) reason a botanical name can get changed. As we have seen, species that are closely related to each other because they share a common ancestor are grouped into genera. But what mortal knows precisely the evolutionary history of a wild plant? As plant taxonomists gather more data, they refine their taxonomies and they may come to realize (for example) that a grass they had thought was related to other grasses in the genus Stipa is actually more closely related to grasses in the genus Nassella. So, when they take Mexican feather grass out of Stipa and place it in Nassella, the name changes from Stipa tenuissima to Nasella tenuissima.
Family names are capitalized and end in “aceae” except for eight families that were grandfathered in with older names. For those eight families, there are two accepted, correct names! You can use either one.
The eight families that have two accepted names are:
palm family - Palmae and Arecaceae
grass family - Gramineae and Poaceae
bean family - Leguminosae and Fabaceae
cabbage family - Cruciferae and Brassicaceae
garcinia or mamey family - Guttiferae and Clusiaceae
carrot family - Umbelliferae and Apiaceae
mint family - Labiatae and Lamiaceae
aster family - Compositae and Asteraceae
Note from the heirarchy above that the crabapple is in the rose family, Rosaceae. Even though they don't look much alike, apples and roses are closely related. (You should never, however, compare apples and oranges.)
When Robert Frost learned how many different species were in the rose family was he was moved to write a poem:
THE ROSE FAMILY
The rose is a rose,
And was always a rose.
But the theory now goes
That the apple's a rose,
And the pear is, and so's
The plum I suppose.
The dear only knows
What will next prove a rose.
You, of course, are a rose -
But were always a rose.
Botanical Names Below the Species
Plant taxonomists sometimes subdivide species into subspecies, varieties and forms.
A subspecies is a distinguishable, geographically separate population within a species and seems to be almost a separate species. Given more time, a subspecies might evolve into a separate species, but for now the members of different subspecies are still capable of interbreeding where their ranges meet. You cannot have more than one subspecies of a species in the same place, because they would interbreed (they ARE the same species) and the differences between them would disappear. Subspecies names are written in italics and preceded by the abbreviation "subsp." Magnolia macrophylla subsp. ashei - Ashe's magnolia is a subspecies of bigleaf magnolia occuring in the Florida Panhandle. (Subsp. macrophylla occurs to the north of Florida.)
A botanical variety is a distinguishable variant which occurs in the same populations as ordinary examples of a species. Variety names are written in italics, and preceded by "var." The botanical name for the Alabama cherry, a variety of black cherry (also in the rose family), is Prunus serotina var. alabamensis.
The botanical form or forma is the lowest rank in the taxonomic hierarchy. Members of a form are usually distinguished only by very minor characters such as flower color or leaf shape. They can occur anywhere within a species' range, and sometimes are determined by environmental factors rather than genetic. Gleditsia triacanthos f. inermis is the name given to thornless specimens of the usually very thorny honeylocust.
Hybrids, or crosses between different species, are given unique names that are preceded with an X: Forsythia X intermedia. The X is not pronounced, but replaced with "the hybrid species." In this case “Forsythia, the hybrid species intermedia.” The name tells us that Forsythia X intermedia is a hybrid between two species, but, unfortunately, it doesn't tell us which two species. You can also have hybrid genera such as X Amarygia, pronounced, “the hybrid genus Amarygia.” (It was created by crossing Amaryllis belladonna and Brunsvigia orientalis.)
A cultivar (CULTIvated VARiety) is a distinguishable variety that is maintained in cultivation. It can also be called a "selection." Cultivar names may or may not be Latinized, but they are set off in 'Single Quotes' and Capitalized. They are not written in italics. The cultivar name comes after the common name: Flowering dogwood 'Purple Glory' or after the botanical name: Cornus florida 'Purple Glory', or you can put it before the common name: 'Purple Glory' flowering dogwood. Juniperus communis var. depressa 'Aurea' is a yellowish cultivar of ground juniper, which is a variety of common juniper.
Sometimes cultivars within a species are organized into groups, based on shared similarities. Group names are Capitalized and followed by the word "group", but they are not italicized nor set off with quotation marks. Brassica oleracea Capitata group includes all the many cultivars of heading cabbage; the various kales are Brassica oleracea Acephala group, and the many cultivars of Brussells sprouts are Brassica oleracea Gemmifera group.
Now you know more about plant taxonomy then you thought you ever wanted to know!
But if you STILL haven't had enough, get the official skinny on botanical taxonomy from the International Association for Plant Taxonomy, and the last word on horticultural taxonomy from the International Cultivar Registration Authorities.