Molecular studies place Moraceae within Rosales in a clade that also includes Ulmaceae, Celtidaceae, Cannabaceae and Urticaceae. Cannabaceae was formerly sometimes included in Moraceae but molecular phylogenetic research supports its segregation from it (Sytsma & al. 2002, APG II 2003).
As currently understood the family includes 43 genera and 1200 species (Tison & de Foucault 2014). Most species are woody and confined to the tropics, especially in Asia. Not a single species of Moraceae is native in Belgium but species from at least three genera have been recorded as escapes from cultivation. In addition to the genera treated in detail in this account several others are sometimes cultivated and might occur as escapes. A species of the pantropical genus Dorstenia L. is proliferating in heated greenhouses in the Botanic Garden in Meise. Its exact identity requires further study. D. contrajerva L. is a weed in greenhouses and nurseries in North America (Wunderlin 1997).
The three genera treated below are readily distinguished at the fruiting stage. Since escaped plants rarely flower or fruit emphasis is on vegetative characters which are, however, much less conclusive for their separation.
1 Leaves palmately 3-5(-7) lobed with rough upper leaf surface. Terminal vegetative bud surrounded by a pair of stipules. Fruit a green or purplish druplet surrounded by a fleshy perianth, 50-80 mm, edible (fig) === Ficus
Leaves variable, either entire with serrate margins or 3-5-lobed or a mixture of entire and lobed leaves, with upper leaf surface smooth or rough. Terminal vegetative bud scaly, not surrounded by a pair of stipules. Fruit of several druplets, crowded into a globose or subcylindrical syncarp (not surrounded by an expanded fleshy receptacle) === 2
2 Heavily suckering shrub or small tree. Young branches hirsute with hairs > 0.5 mm long. Leaves always coarsely hairy. Fruiting head orange at maturity, bristly hairy, not edible === Broussonetia
Non-suckering shrub or small tree. Young branches smooth or minutely hairy with hairs < 0.5 mm long. Leaves either smooth or slightly rough. Fruiting head white, red or black at maturity, smooth, edible (mulberry) === Morus
A.P.G. II (2003) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Bot. J. Linn. Soc. 141: 399-436. [available online at: https://onlinelibrary.wiley.com/doi/10.1046/j.1095-8339.2003.t01-1-00158.x]
Sytsma K.J., Morawetz J., Pires C., Nepokroeff M., Conti E., Zjhra M., Hall J.C. & Chase M.W. (2002) Urticalean rosids: Circumscription, rosid ancestry, and phylogenetics based on rbcL, trnL–F, and ndhF sequences. American Journal of Botany 89: 1531-1546. [available online at: https://onlinelibrary.wiley.com/doi/epdf/10.3732/ajb.89.9.1531]
Tison J.-M. & de Foucault B. (coord.) (2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.
Wunderlin R.P. (1997) Moraceae. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, Vol. 3. Oxford Univ. Press, New York: 388-399. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10583]
Zhekun Z. & Gilbert M.G. (2003) Moraceae. In: Flora of China Editorial Committee (eds.), Flora of China, vol. 5. St. Louis: Missouri Botanical Garden Press: 21-73. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=10583]