|Rock whitebeam at the Trondheimsfjord, Norway|
Sorbus rupicola is a member of Sorbus aria agg., which contains 20 subspecies. A key to this aggregate is given in Stace - though be warned Stace states "It is probably impossible to construct a reliable key to the agg."! Stace gives Sorbus rupicola the following characteristics:
- Leaves unlobed or lobed ≤1/20 of the way to the midrib.
- Leaves with a single style of teeth or, weakly, two styles of teeth.
- Leaves with 6 to 9 (rarely 4 to 10) pairs of lateral veins.
- Leaves mostly 1.6 to 2.4 times longer than wide.
- Leaves mostly widest in that half of the leaf furthest from the stalk.
- Leaves usually obtuse (rarely acute) at apex.
- Leaves have dense white hairs on lower surface.
- Fruits 10-15mm across, warty.
- "BSBI List 2007". Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-02-25. Retrieved 2014-10-17.
- "Ecological flora of the British Isles: Sorbus rupicola". Retrieved 2010-07-17.
- New Flora of the British Isles; Clive Stace; Third edition; 2011 printing
- Ennos, R. A.; G. C. French; P. M. Hollingsworth (2005). "Conserving taxonomic complexity". Trends in Ecology and Evolution. 20 (4): 164–168. PMID 16701363. doi:10.1016/j.tree.2005.01.012.
- Robertson, A.; A. C. Newton; R. A. Ennos (2004). "Multiple hybrid origins, genetic diversity and population genetic structure of two endemic Sorbus taxa on the Isle of Arran, Scotland". Molecular Ecology. 13 (1): 123–134. PMID 14653794. doi:10.1046/j.1365-294X.2003.02025.x.