Discovery of a second extant plant of Arran’s False Rowan (Sorbus pseudomeinichii)
Discovery of a second extant plant of Arran’s False Rowan (Sorbus pseudomeinichii Ashley Robertson) ROBERT BLACKHALL-MILES
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recent work visit to Scotland took my partner (Ben Ram) and I to the Isle of Arran (v.c 100) to visit the collection held at National Trust for Scotland’s Brodick Castle and Goatfell Nature reserve. Two aims of our visit were to see revegetation work being done by the ranger team in Glen Rosa and to see all three of Arran’s endemic Sorbus L. microspecies in Glen Catacol, in the north-west of the island. On 15 September 2020 we visited Glen Catacol with the sole intention of observing the whitebeams and rowans growing in the valley. At the Glen Catacol trail head there is a small enclosure planted with the five taxa involved in the complex sequence of hybridisation in the evolution of the three endemic Arran Sorbus. This enclosure presented a perfect opportunity to familiarise ourselves with the taxa found in Glen Catacol: S. aucuparia L. (Rowan), S. arranensis Hedl. (Arran Whitebeam), S. pseudofennica E.F. Warb. (Arran Service-tree) and S. pseudomeinichii Ashley Robertson (the Catacol Whitebeam or False Rowan) in their pristine state. The three unique Arran Sorbus are the result of crosses between S. aucuparia and S. rupicola (Rock Whitebeam), with S. arranensis being an apomictic hybrid between S. aucuparia and S. rupicola; S. pseudofennica being a backcross (also apomictic) between S. arranensis and S. aucuparia, and S. pseudomeinichii being a further backcross (also proven to reproduce apomictically) between S. pseudofennica and S. aucuparia (Coleman, 2014). Sorbus pseudomeinichii was published as a new endemic tree from Arran in 2006 and has leaf morphology intermediate between S. pseudofennica and S. aucuparia (Robertson & Sydes, 2006). Originally three trees were found, two mature and one sapling, however subsequently flooding has destroyed one tree and the sapling is presumed to have been killed by deer
A leaf of the newly discovered specimen of Sorbus pseudomeinichii. Photographs by the author.
grazing. This has left a single mature individual on the streamside of the Catacol Burn, making it arguably one of the rarest trees in the world (Coleman, 2014; Rich et al., 2010). The Catacol Burn has a number of tributaries, the banks of one of these, the Diomhan Burn in Gleann Diomhan, holds the majority of plants of S. arranensis and S. pseudofennica, whilst the upper reaches of the main Catacol Burn, and a tributary of it, holds further plants of S. arranensis and S. pseudofennica as well as the surviving plant of S. pseudomeinichii. On our visit to Glen Catacol we chose to follow the Diomhan Burn to its head to view trees along the entire length of the gorge and then walk over the nearby 527 m hill of Bienn Tarsuinn to Loch Tanna in order to follow the Catacol Burn from its headwaters down so as we could take in all of the trees that Glen holds. To protect the trees from grazing the majority in Glen Catacol and Gleann Diomhan are now growing within deer-proof enclosures with only BSBI NEWS 146 | January 2021
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