Botanical names are the names used for properly identifying a plant as well as for referring to it in an internationally used set of words. Since I’ve seen several cases (particularly on tumblr and Walmart) where it has been misused, I felt a post showing/explaining its use was in order. These are the rules in writing botanical names properly; Note that each naming term is arranged as:
Genus, species, subspecies, variety, form, cultivar
Genus always has the first letter capitalized (ex- Acer saccharinum not acer saccharinum), and all terms except for cultivar are italicized. Subspecies always has the abbreviated ”subsp.” or “ssp.” before it (ex- Lilium pardalinum subsp. pitkinense or Lilium pardalinum ssp. pitkinense), variety always has the abbreviated ”var.” before it (ex- Viburnum plicatum var. tomentosum), form always has “forma” or “f.” before it (ex- Picea pungens forma glauca, or Picea pungens f. glauca). Cultivar is always placed between single quotes and never in double quotes (ex- Hemerocallis x “Happy Returns” is the incorrect way, but Hemerocallis x ‘Happy Returns’ is correct). Subspecies, variety, form, and cultivar are sometimes omitted depending on the plant. A hybrid species (a “species” made through the origin of crossings between two different plant species) name is marked with an “x” before the species name (ex- Platanus × acerifolia is a hybrid species from P. orientalis and P. occidentalis), while a hybrid cultivar will oftentimes be just written with an x without any species name after. Here’s a fake plant as an example of nomenclature being properly used (though it is pretty rare to see these different classifications being used all for one specimen): Florisua coolius ssp. subcoolius var. occidentalis f. alba ‘Giant Beauty’
Genus is a group of organisms (plants is this case) that are closely related and share similar characteristics. For example all plants in the Trillium genus are rhizome-growing perennials that are single flowered, three petaled, and have three leaf-like bracts arranged in a whorl (any plant without those characteristics would not be a Trillium). The plural form of genus is genera. Other examples of plant genera are Pinus (pines), Picea (spruces), Acer (maples), Tulipa (tulips), Rosa (roses), and vice versa (here’s a hefty list of pretty much all plant genera for the curious).
Species is generally defined as the largest group of organisms capable of interbreeding and producing fertile offspring. In the case of plants, this definition isn’t always the best definition for “species” as many different species are capable of interbreeding fertilely (for example Trillium erectum is capable of producing fertile offspring with several other Trillium species). As wikipedia puts it eloquently for this situation, other “differing measures are often used [to classify a species], such as similarity of DNA, morphology, or ecological niche”[source] (in the cases of many orchid species, they are defined from each other by the different pollinators that they are adapted to exclusively attract).
Subspecies is a further division between species, mainly for genetically distinct populations of the same species that are divided by geographical location, by distinctly different habitats and/or by morphology. This classification can only be applied to specimens that normally grow natively in the wild, so a cultivated population of plants that is distinct from the wild subspecies of plants out there would not be classified as a subspecies. For example, the species Maianthemum racemosum (False Solomon’s Seal) has two subspecies; Maianthemum racemosum subsp. racemosum which is found wild only in Eastern North America, and Maianthemum racemosum subsp. amplexicaule which is found wild only in Western North America.
Variety technically has the same definition as subspecies, except that it may also apply to cultivated as well as wild plant populations (I have yet to find a better explanation). Example- Cornus kousa var. chinensis is the chinese variety of the asian Cornus kousa whereas Cornus kousa var. kousa is the japanese variety.
Form designates a group of plants with noticeable yet minor differences from the norm, such as like possessing thorns, being furry, flower colour or foliage colour, etc.. Form isn’t the same as variety or subspecies as several plants of the same population/variety/subspecies will often possess different forms which interbreed. Example- Gleditsia tricanthos is thorny in nature, however Gleditsia triacanthos f. inermis is a thornless form that can sometimes be found among thorny Gleditsia tricanthos populations.
Cultivar is as wikipedia puts it is “a plant or grouping of plants selected for desirable characteristics that can be maintained by propagation”[source]. For the most part cultivar refers to one genetically distinct plant or group of plants, and official cultivars and their names are registered in the ICRA. Cultivars cannot be naturally found in the wild, and as my plant ID professor bluntly puts it “is a genetic freak”. Most cultivars are made through either breeding or by found genetic sports/mutations that were found in a group of normal plants, and many if not most plants found in the garden and farm are cultivars. Most cultivars would not be able to survive outside of human cultivation and would be weeded out from the genepool in the wild as many of the characteristics found in cultivars would be disadvantageous in a wild setting. An example of a cultivar would be Trillium grandiflorum ‘Flore Pleno’; it’s a multi-petaled cultivar of Trillium grandiflorum, and all plants with this label are genetically identical as the flowers are sterile for this cultivar (which would be a HUGE disadvantage in the wild) and must be propagated by vegetive means (division in this case). There are also cases of what are called seed strain cultivars (Grandpa Ott’s Morning Glory and Watermelon Beefsteak Tomato for example), though they are a confusing bunch that I will not explain here as I am admittedly having difficultly finding specific information on, so I strongly recommend not using cultivar as a term for seed-propgated types and instead call them strains unless you find well proven information that speaks otherwise. There is also the mess of “Trademark Names” which are often treated as cultivar names when they are in fact not the plants’ true cultivar name but instead a name made to better market a cultivar under a company (For example, Tiger Eyes® Sumac is a trademark name and is sometimes mistakenly called Rhus typhina 'Tiger Eyes', when in reality it's real cultivar name is 'Bailtiger' so as such should be called Rhus typhina ‘Bailtiger’) .
And that is how you should use/write botanical names! I understand how easy it is to slip up and use botanical names improperly, but at least with this guideline it should be hopefully easier to use them right. I hope that this helps many of you when you’re talking with other gardeners =)