This Saturday the National Arboretum hosted the 22nd annual Lahr Symposium; the Lahr is a one day themed event that investigates some aspect of native plants. A good time was had by all, and we all learned something. Eight interesting speakers explored various aspects of the issue. Nine vendors participated in a sales area featuring the beautiful, the curious, and the obscure. All plant people are covetous and I am as lustful as the next man; for the bog I bought Acorus americanus, iris versicolor, Caltha palustris, Hypericum densiflorum, and a combination pot with Venus-fly trap, Sundew, and Pitcher plant. For the open garden, Rhapidophyllum hystrix, Rhododendron cumberlandense and Rhododendron austrinum an orange form. For the landscape crew I bought another Needle-palm.
In his talk,Tony Avent, owner of Plant Delights Nursery, and possibly the country's preeminent horticultural lecturer, spoke for the affirmative, enthusiastically endorsing the use of cultivars in a wonderful talk lavishly accompanied by awe-inspiring slides showing examples of extraordinary selections of native plants. Dr. Michele Dudash, a professor of evolutionary biology at the University of Maryland responded, not negatively, but with some cautionary observations. She reminded us that simple Mendelian genetics dictate that one of the basic tools for developing culativars, "selfing" (crossing a plant with its genetic homologue), produces a generation with half the genetic variety that would have resulted from an open cross. She explored the literature on the effects associated with planting cultivars in reproductive range of their parent species and it turns out there are effects. "Horizontal" genetic exchange occurs between the two groups ; "vertical" movement of those genes into the progeny of the native population does result in the adjoining population of native plants becoming, over generations, more "like" the cultivars thus decreasing diversity. Further, she noted that often the features that increase the appeal of a plant to us, double flowers for example, may directly correlate to a loss of nectaries, or stamens (because they were transformed into petals) and so decrease pollination or genetic exchange. Decreasing the genetic diversity in a species makes it less adaptable and more vulnerable in general. Apparently we ought to be careful when we make decisions about what to plant where which is, I guess, no surprise to anyone. But we still all want Tony's plants.
Good speakers, good plants, and the Arboretum was, and is, beautiful. Magnolias, Cherries, Flowering apricots, and a host of early spring flowers make this a "must visit" week for Washingtonians and visitors. Thank you, Joan Feely, the Curator of the Native Plant Collection, who has been responsible for the Lahr for almost as long as my adult sons have been alive. Sorry Joan.