Annie Morris shares with us her illustrations of a group of morphologically similar whitebeam (Sorbus) tree species and discusses how she has included the differences that are unique to each.
Words and illustrations by Annie Morris, BSc , Botanical artist and RHS medallist, ABA committee and Education Team member.

How do you illustrate a group of plants which superficially look very alike? My task has been to illustrate a number of whitebeam (Sorbus) tree species which all look the same at first glance. This is part of an on-going project with the University of Bristol Botanic Garden to record rare and endangered plants of the Bristol area.
Whitebeam trees have small creamy flowers which by the autumn have produced bright red shiny berries. In Britain one of our native whitebeams is common whitebeam, Sorbus aria (above). Another species in the same genus is the grey-leaved whitebeam, Sorbus porrigentiformis (below).

These two species are important in an on-going story of evolution playing out in the Avon Gorge, a botanical hotspot of carboniferous limestone on the edge of Bristol. The Gorge has at least twenty one different ‘types’ of whitebeam (species, sub-species and hybrids) many of which are found nowhere else in the world. Research has shown that the evolution of new species probably began with crosses between S.aria and S. porrigentiformis.
Some of the species to arise from this parentage are Wilmot’s whitebeam, S.wilmottiana, White’s whitebeam, S.whiteana, Avon whitebeam, S. avonensis, and Leigh Woods whitebeam, S. leighensis. These trees (shown below) have been confirmed as separate species using DNA analysis but luckily for the artist the trees also show subtle morphological differences.




In my illustrations I have paid particular attention to the backs of the leaves where the difference in outline shape, vein arrangement and colour are diagnostically important. As the leaves move in the breeze the undersides appear white, hence the common name.
I have painted in watercolour having drawn the outlines directly on to the watercolour paper using a graphite pencil. The backs of the leaves I painted with a greyish green, mixed from three colours, French Ultramarine, Transparent Yellow and Permanent Rose. When this was dry, I have created the suggestion of the felted appearance using white gouache.
The berries pose other problems, they are shiny and therefore I needed to leave areas of white paper, and they also have various numbers and arrangements of lenticels which I had to carefully observe.

A distinctively different species of Sorbus tree shown above is Sorbus bristoliensis, the Bristol Whitebeam (above), which has orange rather than the more usual red berries and has leaves which, when fallen, are dark brown. This species arose as a hybrid between round-leaved whitebeam, S.eminens and wild service tree, S. torminalis, both shown below.


With all my illustrations I have shown the features of the trees throughout the year which means that they have often taken twelve months to complete.
The evolution of the Sorbus in the Avon Gorge is genetically complicated involving diploid as well as polyploid species and something called apomixis, but that is a story for another time.
Annie Morris has a degree in Botany from Bristol University and has been involved in Botanical Art, both as a practitioner and as a teacher, for over twenty years. She is particularly interested in the native flora of the UK having first learnt to identify the plants when growing up on a farm in Kent. She has been awarded three Silver-gilt medals by the RHS.