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Wildflowers, natives not interchangeable terms

As is frequently observed, "wildflowers" and "native plants" are not necessarily synonymous. The former includes a substantial number of introduced species, some of which have been classified as noxious, that have adapted to local growing conditions. These arrive by accident or design and, among the latter, have escaped cultivation. A great number of them arrived with human colonization. Settlers brought familiar species and varieties with them, generally from Europe, or set about hybridizing to meet requirements for their own survival. Others, both agrarian and ornamental, were imported long before science began to be concerned with the consequences of homogenization of the planet.

We discover that still more are native to a more distant part of the continent, but have migrated into new regions for many reasons. They are hybridized for us, genetically engineered for durability, or simply hitchhike in agricultural packages. Even today, experiments for better hybrids manage to break loose from test beds and invade in an ever-expanding circle, limited only by climate and the range of seed dispersal. Their success is oftentimes at the expense of critical habitat areas for native plants unable to withstand the colonization of species that do not have the containment checks that tend to keep an ecological system in balance.

Some of our naturalized species are popular for their charm and apparent good behavior. Ox-eye Daisy, Chrysanthemum leucanthemum; Evening primrose, Oenothera grandiflora; Kentucky Bluegrass, Poa pratensis; Common periwinkle, Vinca minor all leap to mind. At the risk of being too obviously facetious, who among suburban lawn enthusiasts doesn't mind a lot of Taraxacum officinale punctuating the turf (yes, common dandelion)? But as with T. officinale, all too many have long worn out their welcome and have become a matter of environmental concern. Hopes for eradication fade as a consequence of limited funding for removal and priorities understandably high in related arenas.

Native plants are considered to be those indigenous to the locale in which they are growing. Of course, that doesn't mean for all time; evolution and climate changes over millennia have vastly rearranged the natural landscape, and even today there are species that will touch off sharp debate among those who are fussy about such things. Even contemporary distribution maps aren't necessarily precise; a considerable number of state maps can show a species growing in all but two or three isolated counties, which suggests only that when the data were assembled, the count was zero for those few locales.

In nature, seeds are continually on the march for suitable habitat and plants evolve to adapt. It's therefore possible, for example, that Tiarella cordifolia may have originated in perhaps New York State thousands of years ago and eventually migrated to Florida, parts of Canada, and outward to the Midwest and still be considered native in all locations. During the most recent ice age, almost any species of plant would have found parts of Pennsylvania to be inhospitable, for it was under a mile or more of solid ice, and even after the glaciers withdrew the scarred ground was in permafrost for an estimated 5,000 years. Tiarella lineage in northern Pennsylvania, can't possibly be more than 6,000 years, having been introduced by wind, water, birds, animals from somewhere else, perhaps even the vast sheets of ice that slithered across the Allegheny mountains.

Confounding the identity of natives, which by definition are adapted to the habitat in which they are traditionally found, is the present climate change. Kalmia latifolia, which enjoys dry acidic uplands, is in slow retreat northward as temperatures rise, and over the next few decades Pennsylvania's treasured Mountain Laurel may become a New Yorker.

Yet debate rages on. At worst, one native plant directory might call it introduced while another asserts it's indigenous. At best, it might be a native to a neighboring state, but uncertainty allows it to be included in a native-to-state collection on a probationary basis.

Decades ago, enthusiastic faculty at the University of Pennsylvania set about to construct the complete distribution list of plants in the commonwealth and to attempt to untangle lineage. Their work, which lives on today in a very helpful online database, is about as thorough as we might reasonably expect and a towering testimony to mapping before the support of contemporary technology. For lack of anything more substantial, we opt to rely upon it as a sufficiently final word to draw conclusions about the regional and local habitats.

Clearly, it's an inexact science and of only marginal importance to all but the ultra-purist. The resulting latitude may be comforting those among us who are fond of a species native to the broader area, but perhaps not a specific back yard.

Although a county and state list may differ, many habitats are sufficiently common to permit us to include species in the collection that likely do not belong; should they naturalize and make their way into the forests to thrive, they have either become "wildflowers" and interlopers at the same time or perhaps an ancient elimination of a native has been corrected and the woodland restored.

On a national scale, the USDA's plants database could be considered the most authoritative, although it responds best to a specific species request; University of Pennsylvania can identify species that are grouped for such conveniences as county, native vs. introduced, and wetland indicators, and it has served as a resource for us.

We find satisfactory starting points for any region through native plant societies, conservation organizations, and environmental offices. Typically these list the most commonly available species and those with which the gardener is likely to enjoy success, perhaps one or two percent of possible species. Anxiety about this limitation is not needed; the remainder may not be available in the commercial marketplace and many grow in such restricted environments that success in a traditional landscape would be at best difficult.

The current and out-of-print book market then serves to round out more detailed research opportunity for those of us in quest of greater challenges.

References:

National Resources Conservation Service (USDA) Plants Database

The Pennsylvania Flora Project (Morris Arboretum/University of Pennsylvania)

Rhoads, A.F., and Block, T.A. (2000). The Plants of Pennsylvania - An Illustrated Manual Philadelphia: The University of Pennsylvania Press.