Aria rupicola

Aria rupicola, commonly known as rock whitebeam, is a rare species of shrub or small tree best known from the British Isles but also reported from Norway, Sweden and Russia.

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

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).

Stace gives Aria 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.