Sorbus rupicola

Sorbus rupicola, known as rock whitebeam,[1] is a rare shrub or small tree best known from the British Isles but also reported from Norway, Sweden and Russia.[2]

Sorbus rupicola
Rock whitebeam at the Trondheimsfjord, Norway
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Rosales
Family: Rosaceae
Genus: Sorbus
Subgenus: Sorbus subg. Aria
Species:
S. rupicola
Binomial name
Sorbus rupicola
(Syme) Hedl.

Reaching heights of 10 m,[3] it grows in rocky woodland, scrub and cliffs, usually on limestone.[3]

The species reproduces apomictically (asexually via cloned seeds) and was presumably created by autopolyploidysation of the common whitebeam proper (Sorbus aria s.str.). It contains a tetraploidal set of chromosomes (2n=4x=68).

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."![3] 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.
  • A young specimen
  • Back of a leaf
  • Upper surface of a leaf
  • Upper surface of a leaf
  • Twig and part of a leaf

References
  1. BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
  2. "Ecological flora of the British Isles: Sorbus rupicola". Retrieved 2010-07-17.
  3. New Flora of the British Isles; Clive Stace; Third edition; 2011 printing

Further reading
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