Sessile Oak

The sessile oak (Quercus petraea, Syn: Quercus sessilis Ehrh. ex Schur, Quercus sessiliflora Salisb.), also called winter oak, is a plant species of the oak genus (Quercus) in the beech family (Fagaceae). To emphasize its membership in the oak genus, the hyphenated spelling Sessile Oak is commonly used in botany. The sessile oak was Tree of the Year 2014 in Germany. In common parlance, a tree is understood to be a woody plant consisting of a root, a tall trunk rising from it, and a leafy crown. Botany defines trees as perennial and woody seed plants that have a dominant shoot axis that increases in girth through secondary growth of thickness. These characteristics distinguish a tree from shrubs, ferns, palms, and other woody plants. In contrast to their developmental predecessors, most trees also have much more differentiated leaf organs that arise from multiple branched lateral shoots (long and short shoots). The trunk, branches and twigs elongate every year through the sprouting of terminal and lateral buds, becoming lignified in the process and continuously increasing in girth. In contrast to shrubs, it is a special characteristic of trees that the terminal buds dominate over the lateral buds (apical dominance) and thus a predominant main shoot develops (acrotonia). Arborescent life forms occur in various plant groups: "True" trees are the deciduous trees among the angiosperms and the arborescent gymnosperms, which include conifers such as the conifers, but also Ginkgo biloba (as the only extant representative of the ginkgo family) and numerous representatives of the pinnate gymnosperms (Cycadophytina).

The most peculiar tree is probably Welwitschia mirabilis, which is found in Namibia and whose trunk remains in the ground. In addition, the palms and the tree ferns can also form a tree-like shape. However, these groups do not possess true wood (secondary xylem) and are therefore not considered trees. A special position takes the dragon tree (Dracaena). Although this belongs to the monocotyledons, it has an atypical secondary thickness growth.

The age of a branch can be determined from the number of annual shoots and the degree of branching. However, this age determination is complicated in numerous species (for example, spruce or fir) and regularly in older trees by the formation of so-called preventive shoots, which sprout from "dormant" buds. The regular formation of preventive shoots is called reiteration (pronounced re-iteration). These re-shoots serve to renew the crown and provide trees with the ability to replace aging branches as well as respond to stress (snow breakage, insect calamities).

Trees can reach an age of several 100 years, in certain locations even several 1000 years. The oldest tree in the world (as of 2008) is the 9550-year-old Old Tjikko spruce in the Fulufjället National Park in Dalarna County in central Sweden. Three other "generations" (375, 5660 and 9000 years old) with identical genetic material were found under this spruce. The number of spruces over 8000 years old is estimated to be about 20. Thus the spruce is approximately twice as old as the North American pines, which with 4000 to 5000 years were considered so far as the oldest living trees. The demonstrably oldest trees in Central Europe are dated at about 600 to 700 years.