A botanical garden differs from any other garden because it is made up of Collections that have been scientifically identified and arranged according to scientific as well as aesthetic criteria. The approximately 100 thousand square meters that make up the Palermo Botanical garden can be schematically divided into different sectors: some of these date back to the Garden's foundation, others were created after the last expansion at the beginning of the 20th century, while still others were recently planted during the last few decades. The most important sectors are the Linnaeus and Engler Systems, both in terms of their size and the importance of the plants that they contain. They are organized systematically, that is according to different biological classification systems. A few years ago, what was the third largest sector of the Garden, the Experimental Sector, and part of the historic Exotic Arboretum were recently converted to accommodate important systematic and biogeographical collections. These include the Cycad sections, the Palmetum, the Tropical Orchard, and the Physic Garden.