INFLUENCE OF LIGHT-INTENSITY AND WATER-STRESS ON LEAF SURFACE CHARACTERISTICS OF CYNOGLOSSUM-OFFICINALE, CENTAUREA SPP, AND TRAGOPOGON SPP

Leaf surface characteristics of Cynoglossum officinale, Centaurea diff usa, Centaurea maculosa, Tragopogon dubius, and Tragopogon pratensis, important rangeland weeds of Canada, and effects of light intensity an d water stress on these charac- teristics were studied using scanning electron microscopy. Both adaxial and abaxial leaf surfaces of Cynoglo ssum officinale were covered with long, uniseriate trichomes with exte nsive micropapillate sculpturing, The leaf surfaces of Centaurea diffu sa and Centaurea maculosa had two types of trichomes: (i) sparsely dis tributed, multicellular, uniseriate trichomes with ribbon-like chlorof orm-ether soluble extensions at their tips and (ii) glandular trichome s. Centaurea diffusa and Centaurea maculosa cannot be distinguished an the basis of trichome morphology. No crystalline epicuticular wax was observed on Cynoglossum officinale or Centaurea spp. leaf surfaces. C ynoglossum officinale and Centaurea diffusa uniseriate trichomes becam e more abundant as light intensity declined. Micropapillate sculpturin g on Cynoglossum officinale trichomes disappeared at low light intensi ties, Ribbon-like extensions at the tips of Centaurea diffusa uniseria te trichomes increased with increase in soil moisture stress, The leaf surfaces of Tragopogon dubius and Tragopogon pratensis lacked trichom es but were covered with tubular epicuticular wax. Tragopogon dubius a nd Tragopogon pratensis cannot be distinguished on the basis of epicut icular wax morphology. The abundance and size of epicuticular wax crys tals on the adaxial leaf surface of Tragopogon pratensis declined with decrease in light intensity and increased with increase in soil moist ure stress. Such plasticity Of leaf surface morphology may be importan t in the acclimation of these species to harsh environments.