Wild Apple (the artist formerly known as Crab)

Not one of ours, unfortunately! A magnificent crab apple near Crummock Water – but is it a true Wild Apple with capital letters?!

A recent study has suggested we ditch the common name Crab Apple for Malus sylvestris in favour of Wild Apple 1. This is hard to do: it appears all over the place, not least in the field botanists’ bible Stace IV, and in Dony’s definitive English Names of Wild Flowers. Poets (Geoffrey Grigson springs to mind) might make a particular fuss, but as the author of the paper points out, ‘crab apple’ covers a multitude of sins; good for cultural purposes (Shakespeare and jelly) but something of a cloak that has allowed the integrity of this beautiful and charismatic native tree to be diminished by hybridisation in many corners of Europe without us even noticing. In fact, Stace questions the very existence of hybridisation in edition IV of his Flora, but the text had been copied almost unchanged from edition III, dated 2010, now some eight years prior to the recent paper. So keep up! It seems that Malus sylvestris has been hybridising and backcrossing with the cultivated apple Malus domestica – to which it is in any case part ancestor – for some time. Maybe we do need a new name after all.

Last year Dr Markus Ruhsam, the lead author of the paper which looked at crop to wild introgression in apples in Scotland, offered to include molecular analyses of some Herefordshire trees in his work. Five samples were duly sent off for study, all from the western edge of the County. The results have just come back, and they confirm true Malus sylvestris is still present in Herefordshire. I am delighted by this, but surprised: the paper had shown high proportions of hybrid trees even in quite remote parts of Scotland, so little hope, I thought, for an area as intensively-farmed as VC36.

Three of the five samples were shown to be ‘good pure sylvestris’, two from the Upper Olchon Valley, and one from the Birches nature reserve. (In fact, even these had very low levels of the domestica genome, but they were well short of 10%, the value used as a pragmatic cut off between wild apple and its hybrid.)

The Upper Olchon valley also yielded a hybrid tree, ostensibly little different from the wild trees (which were growing 1km and 150m away), and the fifth tree, at HWT’s Crow Wood Reserve, was also shown to be a hybrid. Each of the hybrids had about a quarter of its genome from the cultivated apple.

It is not possible to conclusively identify Wild Apple from its hybrid with Malus domestica on field characters alone, and sometimes not even from Malus domestica itself! Hit rate for the study population (comprising 239 samples of all three taxa) using a mixed bag of characters was only 68%. However, classification in the lowest quintile of leaf hairiness, long known to be a useful character, was subsequently shown by molecular analysis to yield a hit rate of 84% in telling sylvestris trees from the hybrid – that’s five of six trees correct. By focussing on this we perhaps stand the best chance of pinpointing our pure native trees.

In spite of the apparent disagreement about hybrids, Stace IV does focus on this key character. Two of the three Herefordshire trees which molecular analysis showed to be good sylvestris had been sent off for sampling on the basis of their leaves being completely glabrous, whereas it seems to me that most trees which initially catch the eye as Wild Apples end up having fairly obvious hairs on the petiole, sometimes extending onto the vein below.

leaf from tree 3 showing glabrous petiole and under-surface
sparsley hairy petiole typical of most Wild Apple lookalikes

Can I thus ask that anyone recording Wild Apple Malus sylvestris performs this important check, and annotates the record with something like ‘leaves completely glabrous’, so that we can build up a picture of where the trees most likely be our true Wild Apple occur? We may miss some slightly hairy true plants in this way, but it’ll be a step forward. With maximum insect-driven pollination distances typically of the order of 4km, it is perhaps less likely we’ll be finding trees of this sort in the centre and east of the County where so many domestic apples predominate, but as this all goes to show, life is full of surprises.

1 Ruhsam, M., Jessop, W., Cornille, A., Renny, J. & Worrall, R (2018) Crop-to-Wild Introgression in the European Wild Apple Malus sylvestris in Northern Britain Forestry 92, 85-96.

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