Here's a reason. In fact, here are several: cherry laurel, spurge laurel, mountain laurel, Portuguese laurel and California laurel; crape myrtle, wax myrtle, ground myrtle and box-leaf myrtle. Are any of these laurels? Are any myrtles? Not a one.

Botanical nomenclature is a universal language. Gardeners can go anywhere in the world and converse about plants without trying to figure out that "kiss-me-at-the-gate" is a regional name for the herb Saponaria. And I don't even want to know why some people call Campsis radicans "cow itch."

Most of the words in plant names are based in Latin, but many Greek words appear, such as Chaenomeles for flowering quince. Japanese also makes an appearance in words such as Tsuga for the hemlock genus. 

And many scientific plant names contain people's names or the names of places. For example, Viburnum davidii and Davidia involucrata are both named for Armand David, a French missionary to China. Fuchsia is named for the German doctor Leonhart Fuchs. Viburnum x bodnantense is named after Bodnant, a garden in Wales. But don't assume too much: I once thought Cornus florida meant that the Eastern dogwood was native to the state of Florida. In fact, "florida" means profusely flowering in Latin.

The words in a plant name may also describe a quality. The word "mollis" means soft and is an apt moniker for lady's mantle, Alchemilla mollis, because of its velvet-soft leaves. Plant names can also tell what a plant looks like, such as the heart-shaped leaves of Tilia cordata. 

When we talk about plants, we're using a classification system developed in the 18th century by the early botanist Carl von Linné (or Linnaeus). Linné grouped plants according to reproductive characteristics. Today we still use this system though the criteria for classification has evolved. Cascading down from broadest shared characteristics to more closely related are the hierarchy of kingdom, division, class, order, family, genus, species and subspecies. Varieties, hybrids, and cultivars are also related to in the botanical naming system.

The family name ends with "aceae" and denotes some kind of closely related genetic characteristics. For example, Asteraceae is the name of the composite (daisy) family. Sometimes taxonomists refuse to go along with the standardized endings and continue to use the old names for many plant families. That's why you may still see Asteraceae listed as Compositae.

"Binomial" is the term used to describe the two-word plant name. A binomial contains the genus, the next subset of the family category, and the name for the first word. Species (or specific epithet) is the name for the second word and is a subset of the genus category. In the binomial Cornus kousa, Cornus is the genus and kousa is the species or specific epithet. Put the two words together and you have the genus and species of the Korean dogwood. Prunus (plums, cherries, apricots) and Crataegus (hawthorns) are two genera (plural of genus) in the rose family, Rosaceae. Occasionally, a family will have only one genus: Ginkgo biloba is the only member of Ginkgoaceae.

The genus Rosa contains about 150 different species, including our native Nootka rose (Rosa nutkana) and R. mulliganii, named for Brian O. Mulligan, former director of the Washington Park Arboretum.

When there are naturally occurring variations within a species, the species is divided up into subspecies or varieties.  The groups are large, usually separated geographically; the characteristics are markedly different.  The shore pine, Pinus contorta var. contorta, and the lodgepole pine, Pinus contorta var. latifolia, are two extremely different-looking examples of this species.

A hybrid is a cross between two species. Some hybrids occur naturally, such as Arctostaphylos x media, which is a cross between kinnikinnik, A. uva-ursi, and hairy manzanita, A. columbiana.  Some occur accidentally in gardens. Plants with native ranges that do not overlap are able to hybridize when brought into close proximity. This happened with two California species of silk tassel, Garrya fremontii and G. elliptica. They crossed themselves in a garden on the Eastside of Lake Washington, and the resulting plant is G. x issaquahensis. Other crosses are done on purpose to get a better plant--bigger flowers, redder tomatoes. The "x" in the name is a clue that the plant is a hybrid, but that clue is sometimes left out on nursery tags and in books or catalogs.

Rarely, two genera will cross to create an intergeneric hybrid. One example is x Heucherella. Another accidental garden hybrid, it's the cross between coral bells, Heuchera, and one of foamflower, Tiarella. Plants listed as x Heucherella share characteristics of both parents. Note that when the hybrid is intergeneric, the "x" is placed at the beginning of the name.

Beyond genus, species and hybrids, the most common plant name we see is the cultivar--those labels written in single quotation marks, such as the 'Peace' rose and 'Stella d'Oro' daylily.  Cultivars--a contraction of the words "cultivated" and "variety"--are forms of a plant; they don't relate to the scientific classification, but are horticultural designations. 

Cultivars may have a natural origin, such as the pink-flowered form of the Eastern dogwood, Cornus florida. The pink flowering dogwood is a naturally occurring plant that is in the minority, because most Cornus florida trees in nature have white flowers. Pink forms have been taken into regular breeding programs and the result is a multitude of different kinds of pinks. When particularly lovely plants are found and breeders want to make these forms available to us, the plants are propagated asexually, which includes tissue culture, grafting and cuttings, in order to keep the desired characteristic true. These casual variations, such as the pink flowers of a dogwood, do not often come true from seed.

Cultivar names aside, the changeable science of nomenclature is what causes gardeners to throw up their hands in despair of learning plant names. There's no denying that the whole subject is ripe for parody. The Douglas fir (Pseudotsuga menziesii) has had a total of nineteen different names since it first it was collected by Archibald Menzies during Captain Vancouver's 1791-95 voyage. Our dear garden mums were switched from Chrysanthemum to Dendranthema, a change that took place 40 years ago, but took a few decades to sift down to the gardeners' level. But by then, the scientists had heard an outcry from we mere mortals, and the name was changed back to Chrysanthemum. Now it will take awhile for the literature to catch up.

Certainly the most fun with botanical names must be found in Edward Lear's The Complete Nonsense Book (New York: Dodd, Mead & Co., 1912).  Here is where we find drawings such as the one of a delicate, pendulous bloom of what looks like a bleeding heart. But, instead of pink hearts, there's a string of people with their feet tied to the stem; ah, it is of course, Manypeeplia upsidownia. And another shows the triangular porcine bloom of Piggiwiggia pyramidalis.

See, it's not as scary as you thought. Look up a few plant names--plants you have in your garden-- and practice saying them to anyone who will listen. "Here is my Rosmarinus officinalis--that means rosemary was used as a medicinal herb by the Romans, you know." Practice saying them to the cat.  Practice saying them to imaginary visitors. Start dropping the names in casual conversation--"I've so enjoyed my Parthenocissus henryana this year!" It won't take long before you're hooked.