Turner's unlikely and irrepressible oak at Kew Gardens

A little over three months ago (23 May 2024), I was reacquainting myself with a few of my favourite oaks in London. My wife Lynda and I were at the tail end of leading an ASA 'Spring Garden Masterpieces of England and the RHS Chelsea Flower Show' tour, culminating with a morning tour of Kew Gardens by Australian expat, Richard Barley. 

I had got to know quite a few of Kew's trees from my time working there in 2011 and 2012, particularly this one which was - if I detoured slightly - on the way from our home near Kew Palace to my office in the Museum opposite the Palm House.

It's called Turner’s Oak, or more simply, Turner Oak (Quercus ×turneri), a cross between an English oak ...

English oak (Quercus robur)

... and a holly oak (Quercus ilex). 

holly oak (Quercus ilex)

Resulting in a tree with only slightly lobed leaves (here, still light green in late spring) ...

Turner oak (Quercus ×turneri)

An unlikely hybrid this one, between species in two different subgenera of Quercus. English oak is from subgenus Quercus, also known as the New World clade, and holly oak from subgenus Cerris, the New World clade. Despite these clade names, both species grow widely through Europe.

While oaks are rather promiscuous, hybrids are most often between more closely related species. Still, there are plenty of exceptions such as this one. In this case, the natural distribution of the two species overlap but no hybrids have been reported outside cultivation. Indeed, this Turner oak is the only one I've seen.   

It was named from a specimen growing in the nursery of Spencer Turner, in Essex, in 1783, said to have been grafted from the original hybrid growing in the nursery of William Lucombe (where another unusual hybrid, Lucombe oak, emerged). All subsequent specimens of this hybrid have been grafted from that original tree – being a cross between species in different subgenera, it apparently (or generally?) does not produce fertile acorns. 

One grated offspring was planted in Princess Augusta’s 3.6-hectare botanic garden, created in 1759 and expanding later into what became Kew Gardens, part of Royal Botanic Gardens Kew. It grows today near the Princess of Wales Conservatory. 

There are, apparently, Turner oaks with more wedge-shaped, unlobed leaf bases, sometimes sold under the name ‘Pseudoturneri’. Also other variants, many of them presumed to have been grafted from different branches of the original tree grown by the long-lived Mr Lucombe (when he died at the age of 102, he was buried in a home-grown-oak coffin). 

While the species may not be able to reproduce without help from humans, it is resilient. A sign next this still extant Turner oak in Kew Gardens reads:

"In the 1980s the tree was showing evidence of poor health. During the 'Great Storm' of 16 October 1987, it was completely uprooted, lifted a few inches and deposited back on the same spot. This caused the health of the tree to improve markedly: it had been suffering due to compaction of the soil around its roots and this was cured by the uprooting." 

As you can see, in 2024 it is doing very nicely thank you. The addition of mulch to the edge of the canopy also helps reduce compaction from human footfall, as it does for many trees in parks and botanic gardens today. Which means that oaks like Turner oak in Kew Gardens, should outlive a few more generations of nurserymen and botanists.