All living things have scientific names made up of two parts: genus and species. That’s “genus,” not “genius” or “genii.” A genus is a group of closely related species. It’s an organism’s surname (Chinese style): we are Homo sapiens (genus Homo, species sapiens). Many of the names we use to refer to familiar plants are actually genus designations: echinacea, viburnum, aster, rudbeckia all refer to a number of closely related species.
If you’re interested in learning about plants, genus is a useful level of classification. It’s fairly easy to learn to recognize a dogwood (genus Cornus) or a maple (genus Acer) and to learn to distinguish members of that genus from other plants: most dogwoods are shrubs or trees whose smooth leaves have parallel veins, most maples are trees that have 3- or 5-pointed, deeply serrated leaves.
Knowing a plant’s genus gives you some valuable general information about its appearance and growth habits, but it does not tell you what kind of site is most appropriate for that particular species. Within a genus, you can, and you generally do, find species adapted to widely varying conditions. There are viburnums and dogwoods adapted to wet, sunny sites, to dry, shady sites, and to everything in between. So to understand if a plant is right for your garden, you must know the species.
Scientific names are useful because they’re much more precise than common names. If I say “viburnum,” I might mean any one of a dozen native trees and shrubs or any one of a hundred species worldwide. But if I say “Viburnum dentatum,” I can only mean a mid-height shrub with white flower cluster, toothed leaves, and slender stems that lives in wet places throughout the eastern United States–a shrub that will bloom within the next week or so in northern New Jersey.
Plants sometimes have names that include the symbol “x” or words in quotation marks. A plant with a name such as Viburnum x juddii is a hybrid–it was created by crossing plants from two or more closely related species. I tend to avoid hybrid plants, because they are often sterile, and I want pollen to attract butterflies to my garden and fruit to attract birds.
Single quotation marks in a name indicate that a plant is a cultivars (for example, Viburnum dentatum ‘Autumn Gold’). A cultivar is a plant that has arisen in cultivation and been selected for some desirable characteristic, such as larger flowers or cold tolerance, that can be maintained in propagation. Cultivars will cost more than pure species, and it is often illegal to propagate them (kind of like a copyright on a book). They often have undesirable characteristics along with desirable ones. For example, extra-large flowers may mean that the plant can’t stand up straight. Or extra-bright colors may mean that pollinators can’t recognize the flowers. Again, I stick with species whenever possible.
In this blog, in all my writing, in my own garden, and in my horticultural practice I recommend using pure species of plants that are native to this part of the United States. Seek out nurseries that label plants precisely and correctly, and you’ll be more likely to wind up with the right plant for the right place.