Format: ORAL

Ekaterina L. Kotina1,2, Anna V. Stepanova1,3

1 Komarov Botanical Institute, St. Petersburg, Russia 2Saint-Petersburg State Forest Technical University, St. Petersburg, Russia 3The State Hermitage museum, St. Petersburg, Russia

Among the conifer and angiosperm trees, the appearance of bark can vary in a wide range from deeply fissured to smooth one. The bark surface can remain smooth if its outer layers are stretched and/or divided in response to continuous bark increases in circumference as tree grows. We studied different modes of smooth bark formations in several tropical, subtropical (e.g., Adansonia, Commiphora, Euphorbia, Ekebergia, Heteromorpha, Trichilia, Steganotaenia, Sesamothamnus, Vachellia, etc.) and temperate (Betula, Populus, Salix) taxa. Most of these studied taxa share relatively narrow outer bark (OB) and much wider inner bark. The OB usually consists of a thin periderm with lenticels on the surface and a parenchymatous cortex or pseudocortex whose cells contain chloroplasts. This is why we can see a green underlain layer after scraping of bark. This suite of traits is apparently associated with the stem photosynthesis. The anticlinal divisions and tangential stretching of periderm cells, formation of lenticels, and superficial initiation of arc-like periderms can contribute in the maintenance of continuous OB. The sloughing of smooth bark can be performed by peeling or weathering of outermost phellem layers, or by abscission of thin scales formed by superficial periderms. No prominent rhytidome containing the significant amount of non-conducting secondary phloem found in smooth barks. Their cortex or pseudocortex show meristematic activity, occasionally with formation of dilatation meristems. Shifts from smooth bark to furrowed or tessellated one occur in the older portions of stems in most studied species.