Sorbus orientalis Schönb.-Tem.is a taxon that somewhat baffles me. Judging by a pressed example from the Herbarium Berolinese at the Botanic Garden and Museum of the University of Berlin, the tree is very much like the wild service (Sorbus torminalis) with rather broadly lobed leaves (see this link.) I am sure it is the same as Sorbus torminalis var. orientalis (Schönb.-Tem.) Gabrieljan as described in 'The genus Sorbus L. in Turkey' by E. T. Gabrieljan (1961).
This Berlin example comes from the mountains of northern Iran to the south of the Caspian Sea, but a similar from has been described by De Langhe et al. (1973) from Lorraine: On observe très rarement en Lorraine des individus dont les feuilles ont des lobes courts et arrondis au sommet. (Very rarely one sees in Lorraine individuals in which the leaves have short lobes rounded at the end.)
I once found a tree with leaves like the Iranian and French forms near Mayshaves in Kent, UK. Not only were the leaves of a distinctive shape, they were of a thinner texture than normal S. torminalis leaves and dried to a paler shade of brown (see below).
I was also given, by Mary Briggs, a herbarium sheet example of a wild service in Harrow Road near Kensal Green, London, collected in 1904 which seems to have similarly shaped leaves (see below).
There are 37 forms and varieties of Sorbus torminalis listed on the Provisional Global Plant Checklist of the International Organization for Plant Information and these include S. torminalis forma orientalis and S. torminalis var. orientalis.
De Langhe et al. (1973) Nouvelle Flore de la Belgique du Grand Duche de Luxembourg, du Nord de la France et des Regions Voisines. Ist edition. Patrimoine du Jardin botanique national de Belgique.
Gabrieljan, E. T. (1961). The genus Sorbus L. in Turkey. Notes from the Royal Botanic Garden, Edinburgh 23, no. 4: 483-496
From: Brussels 1973 by :