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) ----- Error - Cookies Turned Off 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, ----- 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. ---- "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 ----- 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.