Peter Hilton 20112
LEIGH WOOD WHITEBEAMS 12TH SEPTEMBER 2009
Leader: Libby Houston
A select band of BNS members and one visitor from Hertfordshire met for a full day excursion to be shown most of the 19 species and taxa of.Whitebeam(Sorbus) presently identified in the Avon Gorge. However, the special emphasis of the day was to see the 1 new species and 4 new hybrids which have been recently been discovered and described in Watsonia Vol 27 Part 3(2009)- the publication of the Botanical Society of the British Isles(BSBI). These new species and hybrids have been confirmed by DNA analysis at Bristol University. A chart of the evolutionary tree thought to have given rise to these species and hybrids has been drawn up by Bristol University and this was examined at the beginning of the meeting and Grey-leaved Whitebeam(S porrigentiformis) was seen to play a key to the development of many.
We spent the morning examining the Whitebeams to be found on the plateau of Leigh Woods including a number of planted specimens as well as naturally occurring plants of S latifolia, S bristoliensis, S torminalis and S croceocarpa before proceeding to see the first of the new hybrids called Proctor’s Whitebeam(S x proctoris).
Proctor’s Whitebeam(S x proctoris) is a hybrid between Rowan(S aucuparia) and the cultivated S scoparia. Recently discovered, this hybrid has not been found anywhere else in the world. It has a resemblance to Rowan with distinctive bright orangey-red fruit although opinions on a more precise description of colour differed amongst participants.
Walking down the track under Lily Point we reached the towpath and a good specimen of Leigh Woods Whitebeam(S leighensis) was found in full fruit. S leighensis is a new species for the Avon Gorge found only in Leigh Woods. This distinctive tree of the S aria agg had been recorded as ‘Bristol Porrigentiformis’ for some time although it was realised that there were marked differences from S porrigentiformis. S leighensis holds its branches out horizontally and the leaves are angulated upwards. We inspected Quarry 4 where the largest population of S leighensis can be found as well and where specimens of S porrigentiformis, wilmottiana, eminens, anglica and bristoliensis were also seen.
Continuing along the towpath, we were shown a second new hybrid. This was Avon Gorge Whitebeam( S x avoniensis) which is a hybrid of S aria and S porrigentiformis. This S x avoniensis was shaded by a canopy of trees including S aria and S bristoliensis. Only 2 specimens of S x leighensis have been identified, the other growing on open Carboniferous limestone at St Vincent Rocks.
From the towpath at the base of Nightingale Valley we were asked to look across the river to the Great Fault adjacent to Bridge Valley Road. A lovely specimen of S croceocarpa laden with orange fruit could be seen just above the Portway and to the left at the base of a mudslide the third new hybrid- Robertson’s Whitebeam(S x robertsonii), which is a hybrid of S aria and S eminens, was just visible. Only 1 specimen has been confirmed.
We proceeded to scramble upwards from Nightingale Valley to reach the edge of Quarry 1 and with some difficulty reached a viewing point to see the fourth new hybrid, Houston’s Whitebeam(S x houstoniae). This is a hybrid of S aria and S bristoliensis and the leaves have a similarity to S bristoliensis although rather broader and the fruit although not seen are apparently orange-red. This sole plant grows on the vertical Carboniferous Limestone cliff below Stokeleigh Camp and is inaccessible without ropes. This was named after Libby who first discovered it. Tim Rich(one of the authors of the Watsonia article) described Libby as the ‘guardian angel’ of the Avon Gorge. Libby was especially delighted to show us this tree. Nearby were growing specimens of S whiteana and S bristoliensis.
The meeting finished at 5pm when the group reassembled on safe ground at Stokeleigh Camp.