Use of rare trees and shrubs in horticulture: a strategy for increasing diversity while preserving indigenous flora

Abstract

A small number of perennial plant taxa dominate many horticultural landscapes. This low genetic diversity can lead to greater susceptibility to pests or pathogens, reduce the heritage of local germplasm, and can seem aesthetically mundane. Research is needed to identify new plant taxa that can build diversity but can also be marketed in horticultural commerce as new nursery crops. This paper focuses on the genus Dirca, which comprises a small number of North American species and the only representatives of the family Thymelaeaceae found in the United States and Canada. Wild populations of Dirca spp. are rare, widely scattered, and confined to ecological niches characterized by a narrow set of environmental conditions. Common-garden trials have been established to examine whether two narrowly endemic species of Dirca could survive and flourish under a range of landscape environments. The results suggest that the two species differ markedly in their tolerance to drought, low winter temperatures, and/or poor soil water drainage.