The Rutaceae family is economically important and accommodates, among others, fruiting trees and numerous ornamentals. In addition to the genera treated in detail in this account many others are popular garden ornamentals and may be found as escapes or throw-outs (or merely as relics of former cultivation; e.g. Choisya Kunth, Dictamnus L., etc.). There are also several recent Belgian observations of Skimmia Thunb. (e.g. http://waarnemingen.be/soort/view/237374) but all probably refer to former plantations.
1 Leaves simple. Leaf stalk winged and articulated at junction with blade. Plant not maturing in Belgium (only saplings observed) === Citrus
Leaves pinnate or 3-foliate (if exceptionally simple, then leaf stalk not articulated) === 2
2 Perennial plant, becoming woody at base, usually less than 100 cm tall. Leaves pinnate, with numerous glands (aromatic). Fruit a 4-5-celled capsule === Ruta
Tree, up to 8m tall. Leaves 3-foliate (exceptionally simple), odourless. Fruit a 2-seeded, winged samara === Ptelea
Chase M.W., Morton C.M. & Kallunki J.A. (1999) Phylogenetic relationships of Rutaceae: a cladistic analysis of the subfamilies using evidence from RBC and ATP sequence variation. Am. J. Bot. 86(8): 1191-1199. [available online at: http://www.amjbot.org/content/86/8/1191.full.pdf+html]
Salvo G. (2010) The origin of plants endemic to the Mediterranean and Irano-Turanian floristic regions: case studies from the Citrus family (Rutaceae). University of Zurich, Faculty of Science. [available online at: http://www.zora.uzh.ch/46444/]
Salvo G., Bacchetta G., Ghahremaninejad F. & Conti E. (2008) Phylogenetic relationships of Ruteae (Rutaceae): new evidence from the chloroplast genome and comparisons with non-molecular data. Mol. Phylogenet. Evol. 49(3): 736-748. [available online at: http://www.systbot.uzh.ch/static/personen/elena_conti_assets/Salvo_et_al_2008.pdf]