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FAMILIES
Taxonomists group plants into families primarily based on similarities in the plant's reproductive structures (flowers, fruits, and seeds). All family names end in the letters 'aceae' and begin with a capital letter.
For example, plants in the Rosaceae family typically have flowers with five petals, or petals arranged in groups of five. Members of the Rosaceae family include: apples, pears, blackberries, raspberries, cherries, plumes, roses, and serviceberry. The Rosaceae family is one of the largest plant families.
Another family is Ginkgoaceae. It is one of the smallest plant families. The famous ginkgo tree, botanically called Ginkgo biloba, is its only member.
BINOMAL NOMENCLATURE
The two parts of binomial nomenclature are the generic epithet, which names the genus and is always capitalized, and the specific epithet, which names the species and is usually lowercase. The generic epithet often honor the person who first found the plant. Other genus names can only be appreciated by those who know mythology. Link
GENUS
Below family is the category known as genus. Within a family, members that are most closely related comprise a genus. Think of it in terms of a human family. Your have your immediate family relatives (husband, wife and children) and distant family relatives (cousins, uncles, and aunts). Immediate family members form a genus. The plural for genus is genera. The Rosaceae family is one of the largest plant families. It has more than 100 genera. The plants that we commonly call roses are members of the genus called Rosa within the Rosaceae family. Apples are also members of the Rosaceae family.
Sometimes the genus portion of a species name is abbreviated. Acer rubrum (red maple) might be listed as follows when used in the same paragraph. A. rubrum (red maple), A. saccharinum (silver maple).
SPECIES
The division below genus is the species. The species name is made up of two parts: the genus name and the specific epithet. For example, within the Rosaceae family is the genus Prunus which includes all the cherry, plum and almond trees. One very specific type of cherry tree is called Prunus tomentosa. Prunus is the genus, tomentosa is the specific epithet. When you combine the genus followed by the specific epithet you get the name of the species, Prunus tomentosa. The genus is always capitalized and the specific epithet is never capitalized.
You never use the specific epithet by itself. For example, you would never refer to the tree called Prunus tomentosa just as tomentosa. Another plant with the same specific epithet is Tilia tomentosa, which is a type of linden tree. Just as the name Rebecca could mean any number or people, the name Rebecca Green tells more preciously who you mean.
What is in a name? A name tells you a lot about a plant when the name is in botanical Latin. A very common deer resistant plant, Juniperus procumbens 'Nana' tells us something. I know the genus of the plant is Juniperus because it is the first word in the name and it is capitalized. All plants that are in the genus Juniperus are evergreen trees or shrubs that need full sun light. The specific epithet is procumbens meaning it grows flat to the ground. The word in quotations, Nana, means dwarf. So even if I have never seen this plant or read about it I know from its name that it is an evergreen that needs full sun, is a ground cover, and is a dwarf or small variety.
CULTIVAR
What is that word in quotes? It is the cultivar name and can be spotted by the single quote marks that surround them and are often named for people or places. Beneath species are the divisions of variety or subspecies, cultivar, and forma. A plant's name may not include any of these divisions. A cultivar is a plant that is somehow significantly different that the rest of the species and this difference is passed on from generation to generation when the plants reproduce. The name is in English. All other names are Latin.
FORMA
Forma refers to a plant that again differs from the species, but these differences may not be passed on to the plant's offspring. The only way to be sure a new plant has the forma characteristic, in this case red flowers every time, is to root a cutting of the original plant. When dealing with a plant that is a forma, you always include the word forma in the name. For example, the weeping form of European beech is called Fagus sylvatica forma pendula.
VARIETY
This leaves us with variety or subspecies. A variety of a plant usually differs from the species in where it grows. For example, sugar maples, Acer saccharum, usually grow from Canada to Georgia and as far west as Minnesota. However, the variety called nigrum grows in Iowa. Variety is abbreviated var. and subspecies is abbreviated subsp. or ssp.
BREEDING
The Offspring of Mixed Plant Marriages IS When two different species of plant are crossed, sexually producing offspring, the botanical name of the new plant is written as a formula. An example of this is Laburnum x watereri. One of this plants' parents is Laburnum alpinum and the other is Laburnum anagyroides. The "x" in the new plants' name indicates it is a cross between two different plant species.
HYBRIDS
Most hybrid plants are the result of controlled breading between two related species, both plants have the same genus. However, occasionally two plants from different genera are bred. In these instances a capital "X" is placed before the name of the plant, which will have a new genus name formed by combining the genus names of the parents. For example, the botanical name for Leyland Cypress is X Cupressocyparis leylandii. It is the child of Cupressus macrocarpa and Chamaecyparis nootkatensis.
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