Shrub or small tree to 8 m, densely branched. Branchlets glabrous, greyish brown. Leaves deciduous, palmately three-lobed, sometimes five-lobed, 2.5–5 × ~8 cm, rather thin and glossy, glabrous or with some sparse hairs; autumn colour limited. Inflorescence terminal, corymbose, lax. Flowers sterile. Samaras similar to those of A. campestre. Van Gelderen et al. 1994, van Gelderen & van Gelderen 1999. Distribution ALBANIA; BOSNIA-HERZEGOVINA; BULGARIA; CROATIA; GREECE; ITALY; MACEDONIA; ROMANIA; SERBIA & MONTE NEGRO; SLOVENIA; TURKEY. Habitat As for the parent species. USDA Hardiness Zone 4–5. Conservation status Not evaluated. Cross-reference K68. Taxonomic note This taxon is supposed to be a hybrid between A. campestre and A. monspessulanum – interesting as an example of a hybrid between members of two sections (Platanoidea and Acer, respectively) (van Gelderen et al. 1994) – but the theory that it is a form of A. ×coriaceum has recently been advanced (le Hardÿ de Beaulieu 2003). The story becomes even more complicated since the parentage of A. ×coriaceum is most likely to be A. opalus × A. monspessulanum, rather than A. pseudoplatanus × A. monspessulanum as usually stated (P. Gregory, pers. comm. 2007).
Admitted even by enthusiasts to be of interest to collectors only (van Gelderen & van Gelderen 1999), Acer ×bornmuelleri is a small tree with features tending towards A. monspessulanum. It flowers abundantly in spring (le Hardÿ de Beaulieu 2003). The finest specimen known is that at the Sir Harold Hillier Gardens, 12.3 m tall, 37.8 cm dbh, in 2004. It is only occasionally available but young plants are sometimes encountered, as for example at Thenford House.