Quantification of concavities in roots of Artemisia tridentata

Many publications have described the eccentric growth (non-uniform growth of secondary xylem) of stems of Artemisia tridentata that results from the death of the vascular cambium. The purpose of the present research was to determine if roots of species of Artemisia also exhibit eccentric growth. Eccentric growth in roots of Artemisia species was manifested as concavities (concave depressions that show a lack of secondary xylem). A total of 324 serial tissue sections from six, two-mm long eight-year-old root segments of Artemisia tridentata ssp. tridentata were analyzed. Roots had between 3.9 and 6.6 concavities per tissue section caused by death of the vascular cambium. Forty-three percent and 59% of all concavities occurred within the first and second year of root growth, respectively. For three roots, one concavity occurred along the entire 2-mm long segment. Concavities in roots occur naturally in roots of species of Artemisia. To our knowledge, this is the first study to describe and quantify concavities in roots of Artemisia.