The 2009 ASHS Annual Conference

Shepherdia rotundifolia is an attractive, drought-tolerant shrub endemic to southern Utah/northern Arizona, and is desired by native plant growers for low-water landscaping.  However, it is difficult to grow and establish in urban landscapes due to limited seed availability, seed dormancy, and sensitivity to over-watering.  The objectives of this study were to: 1) characterize natural habitats of S. rotundifolia for selection of a more adaptable plant for the urban landscape; and 2) hybridize with the related species, S. argentea, which better tolerates wet soils.  Shepherdia rotundifolia has been found in diverse habitats in southern Utah from 1,219 to 2,743 meters.  The species is adapted to extremely well-drained soils with varying amounts of organic matter.  Typically found in open areas, we found a unique population beneath the shade of Ponderosa pine (75% relative light intensity) at 2,743 meters.  The diversity in natural habitat of this species could provide a source of germplasm useful for selection of an adaptable form for the urban landscape.  In summer 2008, S. argentea was reciprocally crossed by hand with S. rotundifolia in its natural habitat in Torrey, Utah.  Only female S. argentea crossed with male S. rotundifolia produced fertile seeds.  Hybrid plants are morphologically intermediate to the parents; the hybrid is more vigorous.  Diurnal stomatal conductance measurements of the hybrid showed similar patterns on sunny and cloudy days, with the highest value at 1000 HR.  Stomata of the hybrid were more sensitive to PPFD than either of the parents, exhibiting higher stomatal conductance than the parents on sunny days.  Responsiveness of the hybrid to light intensities was closer to that of S. argentea.  Shepherdia rotundifolia adapted to high light intensity by closing stomata, showing lowest stomatal conductance on sunny days.  These data suggest that the hybrid might be more tolerant to over-watering than S. rotundifolia.  This study suggests the possibility of selecting a more adaptable form of S. rotundifolia for urban landscapes, particularly from the ponderosa pine understory population.  Study of physiological responses in their natural habitats, and greenhouse studies of S. rotundifolia from different populations may support this hypothesis.  The hybrid is another potential source of germplasm, combining the outstanding form of S. rotundifolia with the capacity of S. argentea to tolerate wetter soils.