Tree species and their names are a product of a two-part plant naming system that was introduced and promoted by Carolus Linnaeus in 1753. Linnaeus' grand achievement was the development of what is now called "binomial nomenclature" - a formal system of naming species of living things, including trees, by giving each tree a name composed of two parts called the genus and the species. These names are based on never-to-change Latin words. So Latin terms, when broken into their respective tree genus and species, are called a tree's scientific name. When using that special name, a tree can be identified by botanists and foresters around the world and in any language.
The problem before the use of this taxonomic Linnaean tree classification system was the confusion surrounding the use, or misuse, of common names. Using common tree names as the only tree descriptor still presents problems today as common names differ greatly from location to location. Common names of trees are not as commonly used as you might think when traveling through the tree's natural range.
Let's look at the sweetgum tree as an example. Sweetgum is very common throughout the eastern United States as both a wild, native tree and also a tree planted in the landscape. Sweetgum can have only one scientific name, Liquidambar styraciflua, but has several common names including redgum, sapgum, starleaf-gum, gum maple, alligator-wood, and bilsted.
A Tree and Its Species Classification
What does "species" of tree mean? A tree species is an individual kind of tree that shares common parts on the lowest taxonomic level. Trees of the same species have the same characteristics of bark, leaf, flower, and seed and present the same general appearance. The word species is both singular and plural.
There are nearly 1,200 tree species that grow naturally in the United States. Each tree species tends to grow together in what foresters call tree ranges and timber types, which are confined to geographic areas with similar climatic and soil conditions. Many more have been introduced from outside North America and are considered to be naturalized exotics. These trees do very well when grown in similar conditions they were native to. It is interesting that tree species in the United States far exceeds the native species of Europe.
A Tree and Its Genus Classification
What does "genus" of tree mean? Genus refers to the lowest classification of a tree before determining the related species. Trees of the genus have the same basic flower structure and may resemble other genus members in outward appearance. Tree members within a genus can still vary significantly in leaf shape, style of fruit, the color of bark and tree form. The plural of genus is genera.
Unlike common tree names where the species is often named first; for example, red oak, blue spruce, and silver maple - the scientific genus name is always named first; for example, Quercus rubra, Picea pungens, and Acer saccharinum.
The Hawthorn tree, genus Crataegus, leads the tree genera with the longest list of species - 165. Crataegus is also the most complicated tree to identify down to the species level. The oak tree or genus Quercus is the most common forest tree with the greatest number of species. Oaks have some 60 related species and are native to nearly every state or province in North America.
North America's Species-Rich Eastern Forest
Eastern North America and most particularly the southern Appalachian Mountains claim the title of having the most native tree species of any area of North America. Seems like this area was a natural sanctuary where conditions allowed trees to survive and multiply after the Ice Age.
Interestingly, Florida and California can brag about their total number of tree species which were, and are, transported into these states from all over the world. One may cringe when someone asks them to identify a tree from these two states. They know immediately that it will be a word search of a bountiful tropic tree list. These exotic immigrants are not only an identification problem but also an invasive problem with future negative habitat change.