Shanna Ludwig at the School of Biological Sciences of the University of Bristol is embarking on a PhD research project on "Breeding systems, pollen flow, and continuing evolution in Avon Gorge Sorbus."
http://www.bristol.ac.uk/biology/person/index.html?personKey=VJOZFaoLZgF7ACrYxVEr5eayIz39KO
On her web site Ludwig points out that 19 Sorbus taxa including endemics and hybrids have been recorded from the Gorge and that four species are on the IUCN Red List of endangered plants.
She also gives a brief but fascinating account of some of the reproductive permutations of the trees that result in such a complex array of taxa in one area. The endemic Bristol whitebeam (Sorbus bristoliensis) for example, apparently needs pollen from the common whitebeam (Sorbus aria) to produce viable seed via a process known as pseudogamy.
W. O. Focke, a German doctor who did much work on plant breeding in the late 19th and early 20th centuries, defined pseudogamy as the process where pollen of a different species from the mother tree simply stimulates the production of the outer parts of the fruit within which a parthenogenetic, unfertilised but viable seed is able to develop.
Ludwig points out that the pollination systems employed by the various Sorbus species are pivotal to their continuing evolutionary process. Her research should therefore make an important contribution to the rapidly escalating debate on the causes of evolution being conducted with growing stridency globally among science and philosophy academics and (Heaven forfend) creationists, as well as giving a better understanding of this fascinating diversity of trees in the Avon Gorge.
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