Flowering Branches Cause Injuries to Second-Year Main Stems of Artemisia tridentata Nutt. Subspecies Tridentata

• Published in: Western North American naturalist 2012-12, Vol.72 (4), p.447-456
• Main Authors: Evans, Lance S., Citta, Angela, Sanderson, Stewart C.
• Format: Article
• Language: English
• Subjects: adverse effects; ancestry; Artemisia; Artemisia tridentata; Branches; Cambium; cork; death; determinate growth; Eccentric behavior; Ecosystems; Flowering; Flowers & plants; Growing seasons; Health aspects; Pith; Plant growth; Plants; seeds; stem elongation; Stems; Studies; Tridentata; Vegetation; wood; Xylem
• ISSN: 1527-0904; 1944-8341
• DOI: 10.3398/064.072.0404

Eccentricity of stems of Artemisia tridentata Nutt. (big sagebrush) has been reported previously. Analysis of samples observed over 2 years documented that each stem terminal produces about 8–10 branches each year, and during second-year growth, 3–8 of these develop into short, flowering, determinate branches. Each flowering branch produces hundreds of seeds and then dies at the end of the season, while the other vegetative branches persist. However, growth of the determinate flowering branches causes the death of vascular cambium surrounding their attachment points on the main stem. This death then results in the observed eccentric growth of the stein. In a separate experiment, when presumptive flowering branches were removed prior to elongation, the vascular cambium of the stem was not destroyed, and no eccentric growth occurred. Since the vascular cambium is responsible for continued wood production, the effect of these areas of cambial death is amplified during subsequent years and leads to weak stem segments and possibly to limitations on overall growth. Nevertheless, in spite of these negative side effects, flowering stem growth provides for ample seed production year after year. This peculiar eccentric growth phenomenon, coupled with the anomalous interxylary cork that has also been reported for Artemisia tridentata, supports the idea that this and related species are descended from an herbaceous ancestry and have therefore evolved their rather imperfect woodiness secondarily.