thoughts on oak hybrids, English Oak and Cork Oak

I'm working on hybridizing Q. robur with Q. suber. I'm in the PNW, zone 8, trying to develop an oak that will be more drought tolerant during the summers but will also be evergreen during the Winter.

" The legendary discovery of Ambrozy's wintergreen oak in an old plantation of sweet chestnuts at Horné Lefantovce near Nitra in 1909 has a similar history. According to the legend one day in February some woodcutters were seen in a tavern wearing sprigs of green oak in their hats. This alerted Jozef Misák to the existence of a special tree growing near the garden of a former monastery. The tree was probably a hybrid of an evergreen oak (Quercus suber L.) crossed with a deciduous oak (Quercus cerris L.) Although there was initial talk of an acclimatized cork oak, its hybrid origin has now been confirmed as definite. Sadly, all the trees of this kind that had subsequently been grown at Mlynany disappeared from the arboretum after it came under state control. Ambrózy had propagated it profusely and it is thought that as many as 200 of them once grew in the park. Today the arboretum has only one specimen which was reintroduced from stock held by the well-known Hillier Arboretum in England. "

History | Arborétum Mlyňany SAV

The picture of the leaves does look like it is a cross of Q. suber. If that is a hybrid between Q. suber and Q. cerris, and if Q. cerris can hybridize with Q. robur, then it would stand to reason that Q. robur would be capable of hybridizing with Q. suber.

Lucombe oak is believed to be a hybrid between Q. cerris and Q. suber, and is grown in many botanical gardens.

"Putative hybrids between Q. cerris and Q. robur have been recorded in Britain - currently the subject of an MSc research project" although at the bottom they write that these suspected hybrids could only be the pure species Q. cerris.

Quercus cerris | BSBI Species Accounts

" crosses in progencies from three Q. ilex x Q. suber hybrid trees in mixed forests. "

https://www.google.com/url?sa=t&sou..._AjIQFggtMAE&usg=AOvVaw39vkA5wJxsvGGvGKNln7HZ

Q. ilex x Q. robur hybrid:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2003.01169.x/full

The results of the experiment are strong evidence that this is indeed a hybrid between the two species.

"It turned out that the Q. ilex x Q. suber mating resulted in a seed set of 25%, while the reciprocal cross did not result in any accorn production (Table 2.1). This was attributed to inability of pollen tubules of Q. ilex to penetrate the stigmatic surface after germination." (p22)

http://www.euforgen.org/fileadmin/t...blications/Quercus_suber_OpenSourceCR_web.pdf

(they also reference Staudt 2004)

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Q. ilex can hybridize with Q. robur, and Q. ilex can also hybridize with Q. suber, apparently.

(implication: maybe Q. robur can be compatible with Q. suber)

according to Wikipedia:

" Q. × turnerii Willd. (Q. ilex × Q. robur) (Turner's Oak), a semi-evergreen tree of small to medium size with a rounded crown; it was originally raised at Mr. Turner's nursery, Essex, UK, in 1783. An early specimen is at the Royal Botanic Gardens, Kew. "

from the earlier article:

" Quercus × turneri ‘Pseudoturneri’ is a hybrid between Quercus ilex L. and Quercus robur L. originally produced in England at the end of the nineteenth century. Three individuals of this hybrid are growing in the Arboretum of the BFH, Institute for Forest Genetics and Forest Tree Breeding, Großhansdorf, Germany. "

" The present study clearly demonstrates that introgressive hybridization between a monoterpene- and isoprene-emitting oak species results in a mixed isoprenoid emission pattern combining the isoprenoid chemo-type of both parental species. "

Plant, Cell & Environment, Hybridization of European Oaks (Quercus ilex x Q. robur) results in a mixed isoprenoid emitter type, J.P. Schnitzler, R. Steinbrecher, I. Zimmer, D. Steigner, M. Fladung, Volume 27, issue 5, May 2004, pages 585-593,

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Hybridization between different sections of oak are possible, but apparently only if Q. suber is acting as the pollen parent.

http://www.nature.com/hdy/journal/v102/n5/full/hdy20098a.html

Sexual reproduction in the cork oak ( Quercus suber L). II. Crossing intra- and interspecific barriers

https://www.ncbi.nlm.nih.gov/pubmed/11555243

Although Q. ilex is a Mediterranean evergreen oak, it is grouped together in the White Oaks section with Q. robur.

Q. suber is grouped under the section Cerris.

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"The presence of fertile oak hybrids resulting from interspecific crossing between more than 500 species recognized in the genus is well-known, and has been extensively documented (Govaerts and Frodin 1998 ). The inter-sectional hybrids in Quercus L., are frequently sterile, such as Q. robur (Sect. Robur) cross to Q. suber (Sect. Cerris) ... " It goes on to say that, of the more than 300 oak hybrids that have been acknowledged, 70% of them are fertile, capable to generate viable offspring, and showing the ability to backcross.

Oaks Physiological Ecology. Exploring the Functional Diversity of Genus Quercus L. , edited by Eustaquio Gil-Pelegrín, José Javier Peguero-Pina, Domingo Sancho-Knapik, p241

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additional comment from someone else:

My name is Dave. I was the guy in charge of planting 9,000 trees around the Apple Park Campus. About 4,000 of them were oaks of more than 60 taxa. My website is www.oaktopia.org. My iNaturalist page is: https://www.inaturalist.org/observations?place_id=any&user_id=oaktopia&verifiable=any


I thought I'd throw in some direct experience with intersectional hybrids after having grown tens of thousands of oaks of dozens of different taxa. My learning laboratory initially was the Shields Oak Grove at Univ. of California Davis, the Stanford University campus, and anywhere else I could either plant an interesting tree, or find an interesting and unknown tree.


My first oddball oak was a super random Q. x hispanica in the Don Ramos Park in Palo Alto. Took me a month to ID the tree. It's on my iNaturalist page. This discovery opened the door to many subsequent discoveries.


Regarding intersectionals.

For this discussion, probably the most interesting observation concerrns Q. tomentella (Island Oak - CA super rare native) and Q. ilex. After learning that Q. tomentella grows over wide areas of California, I sought them out. Found a nursery that had a bunch, and went to look. And all of them looked as much like Q. ilex as Q. tomentella! There were nearly 100 trees in the block, all intermediate. I got into quite an argument with an 85 year old nurseryman over it. Years later, I learned where he got his seed - and it was from an authentic island-sourced Q. tomentella, except that mother tree was surrounded by Q. ilex!

Then I moved to Santa Barbara, and found more of these tomentella x ilex all over town. As I spoke with other professionals about this oddity, I received confirmation these hybrids were being seen all over the state.

So I bought 50 of the hybrids, and grew them for 5 years. Some of them were heavy acorn producers, and we attempted to grow seedlings. But, as noted elsewhere in the science listed here, the acorns either didn't germinate, or gave incredibly weak offspring.

The hybrids themselves are actually pretty nice ornamental trees, being rather better than either parent in an ornamental setting. But there is of course a fair bit of variability.

My other experience in intersectionals comes from the Shields Oak Grove. The biggest trees are Q. castaneifolia (though European oak collectors pointed out that they are actually Q. castaneifolia x cerris from the giant mother tree in Kew Gardens). Regardless, I've grown upwards of 5,000 seedlings from these trees over the last 15 years. The seedlings turn out to be quite variable in leaf shape and growth habit. And, many of the seedlings showed an enlarge central leaf sinus. Wonder how that got there?

Might it be related to the enormous Q. macrocarpa located 200 feet away, across a big lawn? The Int'l Oak Society people I showed the trees all said it was just Q. cerris showing up, and in fact they all just call these hybrids Q. cerris from looking, which does not fit well with the actuality of these trees. Interestingly, the vigor on these trees is pretty much off the charts - we see 5 feet per year with decent watering and soils. Super vigorous. Haven't done progeny testing on these - that will be interesting.

In the Shields Grove is also a Q. trojana which everyone I've talked with agrees is actually Q. trojana. A lovely little tree shown on my iNaturalist page. But again I've grown thousands of nice seedlings, and almost all of them have an enlarged central sinus!

And what are the trees growing next to that lovely little Q. trojana? More Q. macrocarpa.

But these Q. trojana seedlings are much more uniform than my the Q. castaneifolia hybrids. And they also show excellent vigor. I'm seeing what looks like an intersectional hybrid with good vigor, which might suggest greater genetic affinity than currently recognized. Haven't done the progeny testing yet on these either.

As for the hybrid that started the thread, suber x robur, it's not really of interest to me. Having grown upward of 1,000 Q. suber, I know all too well that they are semi-evergreen, not evergreen. They drop their leaves sometime in March typically, and it takes them 4 to 6 weeks to get their leaves back. In the meantime, it's always fun to field inquiries from clients asking why all the Cork Oaks suddenly died....

And we get hideous sooty mold and honeydew drip off Q. robur throughout coastal California with our enhanced marine layer.

I do like Q. x hispanica, and have actually managed to grow four of them by collecting acorns off a Q. suber in the Shields Grove that was literally growing next to a Q. cerris. But no Q. x hispanica are truly evergreen.

For my evergreen trees, I turn to nature, and look south. Into the Madro-Tertiary flora with dozens of well-adapted evergreen oaks. Q. hypoleucoides is just going into commercial production in California, thanks to my efforts, along with Q. rugosa and Q. oblongifolia. The trees we really need in California are in the Sierra Madre of northwestern Mexico, one of the noted global Quercus hotspots, but the entire area is cartel controlled and considered highly dangerous.

 

The reports of Pedunculate Oak Q. robur (Sect. Quercus) with Turkey Oak Q. cerris (Sect. Cerris) are almost certainly erroneous. I'm not sure where BSBI got them from, but I've not seen any evidence anywhere that they exist.

Q. suber is evergreen - if the ones you've seen are not fully so, then they're not true Q. suber. I'd suspect cultivated origin Q. x hispanica mis-sold.

 

Hi, I'm wondering, did you had any luck in producing suber x robur hybrids?

Note that your systematic basics are seriously outdated: Q. ilex is not related to the white oaks at all – the "de-facto expert on [North American] oaks" (Nixon KC. 1993. Infrageneric classification of Quercus (Fagaceae) and typification of sectional names. Annales scientifiques forestières 50:25s–34s.) got it desastrously wrong.

From a scientific-evolutionary point of view, it would be extremely unlikely as there are not only part of different sections but subgenera, their last common ancestor lived some 55 myrs ago (at least). To my knowledge there has not been a single genetically confirmed hybrid between the two subgenera of oaks. This applies by the way to any Q. x turneri that were tested (we tested one ourselves), they turned out to be just (morphologically unusual) Q. ilex, no sign of a Q. robur parentage in the sequence genetic markers.

Here's the currently valid systematic paper (which is now used by all oak researchers who deal in systematics)

Denk T, Grimm GW, Manos PS, Deng M, Hipp AL. 2017. An updated infrageneric classification of the oaks: review of previous taxonomic schemes and synthesis of evolutionary patterns. In: Gil-Pelegrín E, Peguero-Pina JJ, and Sancho-Knapik D, eds. Oaks Physiological Ecology. Cham: Springer, 13–38. Free Pre-Print at bioRxiv [major change: Ponticae and Virentes accepted as additional sections in final version]

The English Wikipedia page has been updated accordingly – wasn't me :)

It's pretty simply: on the one hand you have subgenus Cerris, the Eurasian oaks, which include the evergreen tropical-subtropical cycle-cup oaks (sect. Cyclobalanopsis) and the Ilex oaks (sect. Ilex), and the deciduous cork oaks (sect. Cerris), sisters of the Ilex oaks. And nope, Q. suber, is not an evergreen oak, as was long believed (and some still do): it's semi-evergreen, delayed shedding, an adaptation to its habitat, possibly stabilised because of some long passed widespread hybridisation of its ancestors with those of Q. ilex. Its sister species and ancestral form is Q. crenata, the alleged hybrid between Q. suber and Q. cerris.

On the other hand you have the American oaks, subgenus Quercus, which went into Eurasia at some point crossing the high-latitude land bridges. They seem to have started as evergreen, too – golden-cup and live oaks in N. America, sect. Protobalanus and Virentes. But their most species-rich lineages starting to shed their leaves: the red oaks, sect. Lobatae, and the white oaks in a strict sense: sect. Quercus. Then there's sect. Pontica, a strange pair of shrubby, hence, not cultivated as ornamentals, oaks growing close to the tree limit in the Caucasus and its sister on the Pacific coast: Q. sadleriana (probably also not evergreen as said in Wikipedia but delayed shedding: different oak lineages coming up with similar solutions)

But within the same subgenus, there may be a chance, and within the same section (as defined in Denk et al. 2017), it's pretty much guaranteed success for cultivating hybrids.

Regarding the striking similarity between Q. tomentella (subgenus Quercus section Protobalanus) and Q. ilex (subgen. Cerris sect. Ilex). It struck me too (and other oak researchers) but its a pure convergence, albeit a very fascinating one. Again, different subgenera, I would be very surprised if those "hybrids" where any. Note that Q. ilex is extremely variable, also in its natural range, and has a high capacity for propagating itself under the right conditions (a colleague of mine uses the litter of a single Q. ilex tree to confuse biology students: they normally end up with seeing 4-5 species). While our horticulturists and field botanists have described many Q. ilex hybrids across the Meditteranean, there are very few genetically backed ones, and no hard evidence so far for (fertile) F1-hybrids outside botanical gardens.

Genetically, the identification of inter-sectional hybrids is very straightforward. You extract the DNA (there are kits for extracting plant DNA, which don't cost the world) and have a professional lab sequence a nuclear and plastid marker (which is now very cheap) and you know. And Section Ilex has been very promiscuitive in the (distant) past, so much we know from their genomes. But the garden hybrids I know of that have been genetically studied, where all intra-sectional hybrids (Q. castaneifolia, for instance, is genetically just an isolate of Q. cerris, the most variable of all cork oaks, which possibly includes some pseudo-cryptic species).

Q. trojana is genetically much more polymorphic than you can expect based on its morphology; we have ourselves confirmed a morphologically determined F1 hybrid between Q. cerris and Q. trojana in the Naples Botanical Garden using genetic data (both species have private variants that are never found in the other).

 

Fascinating, thanks! Very useful to know that Q. "×" turneri isn't a hybrid at all, just abnormal Q. ilex. Do you have a reference for that, please? It's not mentioned in the Denk et al. paper you cite (which is available in published final form at researchgate).

Worth adding though, that Q. pontica is grown as an ornamental shrub/small tree in Britain. It is very attractive with its Castanea-like leaves.

 

Negative results are usually not deemed to be worth publishing. I only know of those who tried and failed to find anything unusual about it (genetically). So, we cannot say for sure it's not a hybrid, but we also have so far no evidence it is. Morphology is at best an indication for mixing in oaks, but it's really only the genes that don't lie (if we look at putative hybrids between species, we can distinguish unambiguously, of course—such as inter-sectional ones).

As particular as the original English hybrid is, quite similar leaves can be occassionally found in Q. ilex, and their (fossil) precursors. For an overview, check out this (palaeobotanical) paper:

Denk T, Velitzelos D, Güner HT, Bouchal JM, Grímsson F, Grimm GW. 2017. Taxonomy and palaeoecology of two widespread western Eurasian Neogene sclerophyllous oak species: Quercus drymeja Unger and Q. mediterranea Unger. Review of Palaeobotany and Palynology 241:98–128.

Here's two examples from that paper regarding the leaf variation in modern-day Q. ilex. This is all from the same(!) litter sample, which naturally also includes entire-margined ones. The only other other oak showing such extreme leaf plasticity is possible Q. cerris.



Originally the possibility of inter-subgeneric hybrids intrigued us, too, hence, we included x turneri material (from a tree in the botanical garden in Jena, which was supposedly an offspring of the original one in England) in our study on the western Eurasian oaks (and of Q. afares, the Tunesian cork ork, which some considered to be another Cerris x Quercus hybrid: Q. suber x Q. castanea).

Denk T, Grimm GW. 2010. The oaks of western Eurasia: traditional classifications and evidence from two nuclear markers. Taxon 59:351–366.

We got four ITS sequences, they were all Q. ilex (of a relatively rare subtype popping up in France, Italy but also Morocco). Possibly noteworthy: we do have a 15–20 m Q. ilex growing nearby in the park of Chateauneuf sur Loire that has not a single entire-margined leaf (but is also genetically a 100% Q. ilex). We couldn't check the second marker and followed it through, tough, as I had to leave Germany to get "international experience", which ended this line of research. So, the individual is not included in the paper.

 

Excellent, thanks!