Tree - a perennial plant with woody one main shoot (trunk) or woody few main shoots and branches forming a crown in any period during plant development. The trees include the largest terrestrial plants . This group is not a taxon - it groups only plant organisms similar morphologically and functionally. From other woody plants ( shrubs and shrubs ) they differ in having trunk or trunks branching only from a certain height. Trees are sometimes plants that have a chimney instead of a tree trunk ending with a tuft of leaves , i.e. tree ferns, cycads, palms, pandanas, yucca and dracaena. In addition to typical trees and domes, there are also tree succulents (eg some cacti) or woody grasses (bamboos). The botany department dealing with trees is dendrology (gr. Óένδρον - tree). In Poland , tens of thousands of the oldest and most impressive trees are subject to legal protection as natural monuments . In the lexicon or census of plant species, the trees are sometimes marked with the symbol resembling the symbol of Saturn or the alchemical symbol of lead , i.e. double plotted h. (A single plotted h, i.e., means a shrub ). Around 3 trillion of 40 billion trees are currently growing around the world .