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What's the Difference Between Azalea Plants and Rhododendrons?

Linnaeus' Plant Taxonomy: Scientific Names

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Beginners at landscaping and gardening often confuse azalea plants and rhododendrons, as stated on Page 1. The confusion is understandable; for azalea plants and rhododendrons are related. All azaleas are Rhododendrons (note the capital "R"), but not all Rhododendrons are azaleas. Still confused? Well, you're in good company, company that includes the famous Linnaeus. Linnaeus' taxonomy is the standard in botanical classification. Let's have a closer look at the challenging taxonomy of azaleas and rhododendrons, before proceeding to the instructions for caring for them (Pages 3 and 4).

Throughout the following explanation of scientific names versus common names, I will be reminding you to take note of whether I say "Rhododendron" or "rhododendron." With a capital "R," I'm referring to a plant genus. With a lower-case "r," I'm referring to a subset of that genus.

The genus Rhododendron is in the heath family, which also includes its namesakes, the heathers and heaths; blueberries and cranberries; and mountain laurels. Most members of the heath family need an acidic soil in which to grow. When you have a naturally acidic soil in your yard, it's a lot easier simply to grow acid-loving plants rather than trying to change the pH level of your soil.

Scientific Names: Linnaeus' Taxonomy

The Swedish naturalist, Carolus (Carl) Linnaeus established the genus, Rhododendron in 1753. However -- and here's where some of the confusion started -- Linnaeus' taxonomy established "Azalea" as a separate genus. But it was soon pointed out that azalea plants should be considered a subset of the Rhododendron genus, rather than a genus all unto themselves.

Then in 1834 another naturalist corrected Linnaeus' taxonomy on this point. An Englishman, George Don, broke down the genus, Rhododendron into eight sub-categories, composed of numerous species. The azaleas comprise two of these sub-categories (evergreen azalea bushes and deciduous azalea bushes).

Consequently, if you read the scientific name of an azalea, you'll see the word, Rhododendron. That's because azalea plants belong to the genus, Rhododendron -- and the word "azalea" has essentially become this bush's common name. But there are also members of this genus that are just plain "rhododendrons" (note the lower-case "r"). In recent years "rhododendron" has come to be used by gardeners essentially as a common name for those plants in the genus, Rhododendron that have large, leathery, evergreen leaves. The leaves on azalea plants tend to be smaller, by comparison. Within the rhododendrons themselves, leaf-size comparisons are used to make a further division: namely, between elepidotes (large-leaf rhododendrons) and lepidotes (small-leaf rhododendrons).

So how would you be able to identify an azalea, as distinct from a rhododendron? In general, rhododendrons are larger shrubs than are azalea plants, and, as just said, they have larger leaves. Also, in general, azalea flowers have five stamens, while the rhododendron flowers have ten stamens. Finally, unlike rhododendrons, many azalea plants are deciduous.

Now that you've heard about popular varieties of azaleas and rhododendrons -- and have been introduced to the challenge of classifying them in Linnaeus' taxonomy -- it's time to look at how to care for rhododendron and azalea plants. That's the subject of Page 3....

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