Patterns of Variation Among Climatic Races of Red‐Osier Dogwood

Abstract

Red—osier dogwood (Cornus stolonifera Michx.) clones were collected from 21 locations in the natural range of the species and grown in a uniform plot at St. Paul, Minnesota, to determine the extent and nature of geographic variation. Significant variations in plant form and growth rate were noted. Genetic influence among the climatic races was apparent in autumnal phenological events such as onset of rest, change of bark color, and leaf abscission. These events were related to provenance features such as winter minimum temperatures, length of growth season, and to a lesser extent to latitude. The time at which cold hardening began in the autumn differed among clones, but no differences were noted in the ultimate degree of hardiness in midwinter. Spring bud break and flowering occurred at about the same time in all clones, while the loss of red bark color varied. Controlled environment and field tests indicated that photoperiod was the prime factor triggering autumn phenomena, while temperature was most important in the spring.