A double-barreled question frequently asked by amateur botanists and biology students alike is: "Why do we have to learn all those Latin names? Isn't there an easier way?" The response that Latin provides a common language understood by all botanists, regardless of their background, generally falls on unfertile ground. However, an example or two often help make the point. As an example of a very general term, and the confusion that could arise from its casual use, we'll look at “cedar”, certainly a word familiar to most readers.
Even a casual glance at plant references (1) and other general sources, reveals over two dozen different plants that have “cedar” in their names. There are only four “true” cedars, that is, members of the genus Cedrus. Cedrus libani, the cedar of Lebanon and featured on the Lebanese flag, is a tree native to, and once widespread in Asia Minor, but now restricted to only a few populations owing to long time over-harvesting. Cedrus atlantica is the cedar of the Atlas Mountains of North Africa. Cedrus brevifolia, a native of Cypress, is considered by some authorities as a small-leafed form of C. libani. Cedrus deodara, the Himalayan or deodor cedar, is a major timber tree of northern India much prized for its attractiveness and pleasant aroma.
Most of the plants that carry “cedar” as part of their common name are at least conifers (as we'll see below, some aren't). Three species of Juniperus (true junipers) are referred to commonly as cedars: J. bermudiana, a Caribbean native, is called the Bermuda cedar; J. procera, a native of the mountains and highlands of East Africa and the mountains along the Red Sea in Saudi Arabia and Yemen, is called the East African cedar or African pencil cedar; and J. virginiana, the Virginia pencil or red cedar, is a species native to eastern North America. But in Australia the name red cedar also refers to Toona ciliata, a member of Meliaceae, which is not a conifer genus. But it gets worse; Toona ciliata is also known as Burmese or Maulmein cedar in southeastern Asia.
Closer to home (at least mine) is the Western red cedar, one of the main forest species of the Pacific Northwest. Western red cedar is Thuja plicata, which belongs to the conifer family Cupressaceae, along with Juniperus; the true cedars belong to Pinaceae, the family that obviously includes pines. Are we still all together? Good. Now let's consider yellow cedar, another significant forest tree of western North America. Yellow cedar is actually Chamaecyparis nootkatensis, which also happens to belong to Cupressaceae. Moving south along the Pacific coast one may well encounter Chamaecyparis lawsoniana, the Oregon or Port Orford cedar. Changing color now, we find the term white cedar used for the western North American Calocedrus decurrens, which is also called incense cedar; Chamaecyparis thyoides, native to coastal eastern North America; and Thuja occidentalis of the eastern United States. White cedar is a name also applied to some non-conifer species including members of the mainly Asian family Meliaceae: Melia azedarach and Chukrasia tabularis. It gets worse. Chukrasia tabularis is also called bastard cedar by some, and Indian redwood by others. But wait, North Americans know “redwood” as a really big tree in California. We won't go along that route.
This list is beginning to get out of hand, but here are a few other examples from the realm of confers 3 restricted to conifers to avoid quarrels how widely “cedar” has been used: Chilean cedar is Austrocedrus chilensis (Cupressceae), the only member of the genus; Clanwilliam cedar is Widdringtonia cedarbergensis (Cupressceae) from the Cape of South Africa; Japanese cedar is Cryptomeria japonica (Taxodiaceae); and Siberian cedar is actually a pine, Pinus cembra. In order to avoid input overload, I have not included several other “cedar” that have no relationship whatsoever to the true cedars with which we started this exercise. One wonders, perhaps, how grandmother would have reacted to our suggestion that her “cedar chest” really should have been called a 'western red cedar chest' to give proper recognition to Thuja plicata from whose wood it likely came. Mine wouldn't have been at all impressed.
(1) Mabberley, D. J. 1997. The Plant Book, 2nd ed. Cambridge University Press, Cambridge, U.K.