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French Oak Open Days: 8–12 June, 2024
This five-day event included visits to four oak collections in southwestern France and one across the border in Spain. A total of 20 participants took part, including 17 IOS members and 3 members of the International Dendrology Society (IDS). The report below is in two parts: first Jan Awouters gives an account of the Days 1 to 3, then Shaun Haddock covers Days 4 and 5.
Pouyouleix, Passadou, and La Bergerette
by Jan Awouters
The first day we were expected in Arboretum des Pouyouleix for an Oak Study Day hosted in conjunction with the International Dendrology Society. The 27-hectare arboretum is mainly dedicated to oaks and related genera from the Fagaceae. A large part of the arboretum remains covered with the original forest.
Planting started 21 years ago. Currently the collection is composed of 331 taxa: 224 species, 12 subspecies, 9 varieties, 79 hybrids, 6 “question marks”, and 1 cultivar, represented by a little over 900 trees. As the Arboretum is organized geographically, a visit is truly a round-the-world voyage discovering the biodiversity of oaks.
The day started with a presentation by Béatrice Chassé, entitled: “Identifying oaks” (given in French and English!).
So, the first question you need to ask yourself when trying to identify an oak is: “To which of the eight sections in the genus Quercus does it belong?” Simply because if you eliminate sections you reduce in one swoop the number of species you have to think about.
The first step in answering the question is knowing the geographic distribution of the different sections:
- Section Quercus, with about 150 species, grows everywhere oaks grow, except in Indonesia and Cuba
- Section Lobatae, 130 species, only in the Americas
- Section Cyclobalanopsis, 90 species, only in Asia
- Section Ilex, 35 species, distributed in Asia and Europe
- Section Cerris, 15 species, in Asia and Europe
- Section Virentes, 7 species, only in the Americas (and more specifically only in Mexico, Central America, and a few southeastern and southwestern states in the US)
- Section Protobalanus, 5 species, only in the Americas (and more specifically only in northern Mexico and a few western states in the US)
- And finally, section Ponticae, with 2 species, one in northwestern America, Quercus sadleriana, and the other, Q. pontica, in Turkey and western Georgia.
After you have determined the section, you have to try to identify the species. You have to keep in mind that there is enormous phenotypic variation between individuals in the same population and between individuals from different populations. You also have to keep in mind that trees in collections often come from a limited number of individuals, often only one, and that a natural population can be very different.
Finally you need to look at leaves that are growing in the sun, not in the shade, and you need to examine first-flush leaves because second-flush shoots are very vigorous and often have “exaggerated” characteristics for the species, like being more lobed or more dentate.
Following the presentation, our journey begins outside in the section of the arboretum featuring oaks of North America and Mexico.
At the entrance we find Q. emoryi, a species from the southwest of North America. We are all amazed by Q. depressa. This small shrub is currently sprouting with beautiful red new leaves. Other bushy species are Q. miquihuanensis, Q. minima, Q. palmeri, Q. frutex… but after we walk past a small collection of Crataegus and Castanea pumila we come to the real trees: Q. hemisphaerica, Q. texana, Q. viminea, Q. muehlenbergii, and a nice group of Q. phellos that has become very impressive after only 20 years.
Since our guide has done several expeditions all over the world, but especially in Mexico, the collection of oaks from that country is abundant. Quercus pinnativenulosa, Q. acherdophylla, Q. delgadoana, Q. flocculenta, Q. eduardi… are reviewed. Quercus 'Belle d'Aquitaine' is a hybrid between Q. rysophylla and another section Lobatae oak, possibly Q. rubra or Q. shumardii, which was described by B. Chassé and A.J. Coombes based on this tree in Pouyouleix.
Further on, Q. crassipes and Q. mexicana are next to each other. Our guide told us how to easily tell these two species apart. In Q. crassipes, the underside of the leaf bears persistent, ashy gray, flaky stellate tomentum. The 10 to 24 pairs of secondary veins are very protruding, nearly perpendicular to the midvein, and fork to meet in loops before the edge of the blade, and the margin is very thick and distinctly revolute or slightly sinuate.
In Q. mexicana, on the other hand, the reverse bears a gray or pale brown stellate tomentum, powdery and scattered like punctuations, which can be easily rubbed off. There are 6 to 15 pairs of lateral veins that form an acute angle to the midvein and branch out before the edge.
After lunch we discovered Asian and European oaks, including Q. myrsinifolia, Q. salicina, Q. hypargyrea, and Q. longispica, whose underside is covered with a yellowish felt. And while walking to Europe we pass Q. look, Q. afares from Algeria, and Q. infectoria subsp. veneris, just to name a few. At the end of the day we were overwhelmed by all these beautiful and special oaks.
The second day we visited the Arboretum du Passadou, guided by the owner, Jean-Louis Hélardot. Some know him through the Oaks of the world website.
His arboretum was started in 1981 and is nearly two hectares in size with a collection of mainly oaks and maples. More than 500 plants have been planted, and even to this day new specimens are being added.
The arboretum has a fairly extensive collection of hybrids, like Q. ×humidicola (bicolor × lyrata) and Q. ×rudkinii (marilandica × phellos). We saw Q. robur subsp. estremadurensis, also sometimes recognized as Q. estremadurensis, native to Morocco, Portugal, and western Spain. It has leaves that are larger and on the underside hairy and scabrous, with uneven, short, sharp lobes. Quercus laceyi is native to Texas and northern Mexico. The upper surface of the young leaves is pink and tomentose, then glabrous and glaucous. Quercus furfuracea is a rare species, occupying only a few locations across its range. Other species were Q. robusta, Q. hypoxantha, Q. xalapensis, Q. greggii…
Some maple species that we saw were Acer henryi, A. stachyophyllum and A. ×pseudoheldreichii. This taxon is the result of a cross between A. pseudoplatanus and A. heldreichii.1
The group had a late lunch in a nearby restaurant, after which we left for the next day's destination, about two hours south.
The third day we visited Arborteum de la Bergerette, where Shaun Haddock showed us his collection of oaks. Planting commenced in 1990 and at least 200 species of oak can be seen here. The arboretum is 15 hectares in size.
Our walk started at the house where Erythrostemon gilliesii (syn. Caesalpinia gilliesii) and Verbena bonariensis seemed to feel at home in the gravel, judging by the many seedlings that were fully grown. Another notable bloomer was Beschorneria yuccoides, a species of succulent plant belonging to the family Asparagaceae. The inflorescence can reach a height of 100 to 350 cm and the stem and the bracts are red; the flowers are a greenish yellow.
The first oaks we encountered were European species: Q. macrolepis, Q. faginea, and Q. infectoria subsp. veneris. Quercus baloot was collected by Shaun from two different altitudes in the Swat Valley of northwest Pakistan in 1995. Most of the specimens of this oak in cultivation are from acorns of this collection.
To avoid a monotonous list of all the species we saw, I'll discuss some oaks that were remarkable to me. Quercus turbinella is a shrub or small tree native to the southwestern United States and northern Mexico. The leaves are bluish, and only get bluer as it gets warmer and drier during the summer. Other California species we saw were Q. agrifolia var. oxyadenia (for some authors a synonym of Q. agrifolia), Q. chrysolepis, and Q. parvula. We looked at other North American species such as Q. stellata, Q. marilandica, and Q. macrocarpa. Quercus calophylla (formerly Q. candicans) stood out because of its rather large leaves. The reverse is completely lined with a thick tomentum which becomes white as the season progresses.
Another beautiful little oak was Q. greggii. At bud break, the leaves are tomentose, yellowish-green above and whitish below. Quercus kelloggii is rare in Europe. This species apparently does not feel at home in the European climate, but here in La Bergerette there is a remarkable specimen. Finally, we must mention the beautiful group of Q. rysophylla.
An attractive species is Q. dolicholepis from China. The cupules, with long slender scales, are a particularly notable feature, distinguishing it from similar species. Always spectacular, in my eyes at least, are the species with a yellow underside such as Q. longispica.
In addition to all these oaks, we also looked at a number of other types of trees. For example, there was a pine, Pinus patula, which once lost its top in a storm, but as a result the lower branches have settled on the ground and have probably formed roots, so that a low, broad tree has now emerged. Toona sinensis was about to burst into bloom, and Diospyros kaki promised a handsome harvest of fruits.
Lunch was served in the arboretum, kindly offered by our host. Although I didn't get to experience the entire trip, these three days were a learning experience and a reminder that my knowledge about oaks still has a long way to go.
Chocha and Iturraran
by Shaun Haddock
There is a trite saying that if you wish to own an arboretum with beautiful mature trees then you must inherit it, but Michel Duhart, founder in 1975 of Arboretum de Chocha, has a proven alternative: one has merely to live to a great age! Although it was his grandson, Michel de Broglie, who guided us knowledgeably around the 3.5-hectare Arboretum, Michel the elder, now over 100 years of age, joined with his grandson and daughter Nathalie Duhart to welcome us, and later to hand round snacks and socialize after our morning session.
Due to its relative proximity to the Bay of Biscay, the Arboretum, situated in the French Basque country, enjoys an enviable and well-distributed average annual rainfall of 1,300 mm, and Nature provided us with a taster portion of this during the morning. The same factor ameliorates summer heat, with a surprisingly modest average daily maximum in August of only 24 °C. However, strong winds with wet soil can be a problem, and last year five trees were blown down during one wind event.
During his working life Michel spent time in the USA, which, his grandson related, led to Oak Enlightenment on seeing a Quercus falcata in front of a hotel. He duly planted one at home which is now enormous, with foliage cascading right to the ground. In this ideal climate, several other US oaks which were planted at around the same time are now massive and forming a woodland, including Q. texana from New Orleans, Q. phellos, Q. palustris, Q. montana, Q. laurifolia, Q. bicolor and Asian Q. acutissima to name just a sample. In terms of size, however, perhaps the most impressive oak we saw was the largest specimen of Q. rysophylla outside its native haunts, approaching 30 meters in height (enormous was one of the words most frequently repeated in my notes!).
Michel often collected seed in Central America with Francisco (Paco) Garin, whom we were to meet at Iturraran the following day, and as both arboreta are at the mildest end of the climatic spectrum of those we visited, several species we saw only exist in Europe at these two arboreta. Planting here still continues, for instance of Q. benthamii from El Salvador. A 5-meter Q. tarahumara impressed us with its large revolute umbrella-like leaves; a Q. urbani planted in 2005 had leaves on the same pattern but with teeth like a carnivore, whilst the rare Q. brenesii from Costa Rica was evidently of great interest to a quercophile European woodpecker!
Several of the always-handsome Q. castanea caught the eye, but sadly, limited space will not allow a listing of all the rare and interesting Central American oaks to be found at Chocha. However, a more detailed coverage will appear in the Journal in due course.
Although best known for its American oaks, Asian oaks are by no means neglected: a Q. oxyodon approaching 10 meters in height provoked a debate as to whether the nerves were more raised on the left-hand underside of the leaves than on the right. We saw the rare ring-cup oak Q. camusiae, the name commemorating the French monographer of the genus, Aimée Camus (profiled by Béatrice Chassé in International Oaks No. 24).
A large Q. lanata led to a discussion of the differences (or not) between this species and Q. leucotrichophora; a beautiful Q. lamellosa was ornamented with almost white young stems; a large Q. myrsinifolia was forming long acorn strings; whilst a wide Q. mongolica grafted onto Q. robur stock planted next to the North American Q. montana showed how similar and confusing foliage can be!
All in all, it would be difficult even to imagine a greater concentration of large, rare, beautiful, or indeed large-and-rare-and-beautiful oaks, and we sincerely hope we were able to sufficiently show our appreciation of our visit to the two Michels and Nathalie.
The rain in Spain stays mainly… at Iturraran. Nature now disclosed that with yesterday’s showers she had merely been toying with us: today she showed her hand in full with rain all morning. However, undeterred, Francisco (Paco) Garin, who retired as manager 13 years ago but remains an eminence grise of the garden, arrived to guide us on our tour.
In these straitened modern times, when for example the Arboretum National des Barres in France has shamefully been forced to limit access to the public due to lack of funding, the Jardín Botánico de Iturraran seems like a wonderful anomaly—a thriving 25-hectare garden thronged with around 3,000 species of rare and interesting plants supported by the provincial government of Gipuzkoa in Spain’s northern Basque region. The garden is situated in the Parque Naturel de Pagoeta at between 130 and 220 meters above sea level, and has a climate not dissimilar to that of Chocha, with 1,600 mm annual rainfall and only rare frosts, which do not usually descend below -5 °C, although the very occasional -6 or -7 °C has unsurprisingly caused losses. On what was previously farmland, the first plantings were made in late 1987.
The garden contains over 120 Mexican and Central American and 70 North American oak species. There are also hybrids, and one of the first oaks we saw was Quercus ‘Aia’, a cross produced by the rare Q. brenesii, probably with pollen from Q. rubra. Unfortunately, the devil lurks even in the garden of Eden, and some of the rare small plants have had to be deliberately mis-labelled to protect against plant thieves.
As we continued, a huge Q. mexicana of around 26 meters in height showcased the vigor of this species. A large Q. leucotrichophora allowed us to continue the discussion of the day before, as a Q. lanata was planted nearby. The bark of the two trees was very different, that of the former forming pale brown plates. We passed a tall Q. gulielmi-treleasei, and nearby a smaller (but still around 9-meter) Q. acherdophylla. An example of the extremely vigorous Q. meavei planted 12 years ago has reached an estimated 20 meters, and this splendid tree has recently been reintroduced by Béatrice Chassé. A surprise was to see a large Q. incana, as this species is not supposed to enjoy moist conditions, although a steep bank possibly speeds the water past its roots.
We had already seen a splendid Q. lamellosa with huge leaves at the bottom of a slippery bank, but we passed a 7-meter Q. thomsoniana, a close relative of the former from the east Himalaya, a species plentiful in Bhutan, but which I have never seen before “in captivity”.
Francisco eventually shepherded his bedraggled crew back to the Reception Center before departing with our thanks. After recharging with snacks and coffee most of the group left, but five of us who shared a car decided to visit a different part of the garden in the afternoon (they did not have much choice, so I hope it was indeed a democratic decision!). We were immediately rewarded: the rain stopped. Our old friend Quercus sp. put in several appearances on a newly-planted bank as sp.3, sp. 5, etc, but we were then amused to suddenly come across sp. 6480! A small Q. cortesii from El Salvador showed colored new shoots, as did Q. benthamii. The rare Q. irazuensis (for some references a synonym of Q. costaricensis) displayed tropical-looking buttresses at its base. We missed Francisco’s directional guidance, but on our guessed return route we passed the rarely-seen Asian Carya cathayensis.
This is a garden where one could spend days and still not see everything, but with Francisco’s help we were privileged to see a good proportion of the astonishing variety of oaks it contains. A report can only scratch the surface, but muchas gracias Francisco!
Further reading
The collections visited during this event have been written up previously in IOS publications. Follow the links below for more detail on each one:
Arboretum des Pouyouleix
In Our Garden - Béatrice Chassé
Arboretum de la Bergerette
Oaks in a Difficult Climate: Arboretum de la Bergerette - Shaun Haddock
Arboretum du Passadou:
Jean-Louis Hélardot: a Passion for Understanding Oaks - Béatrice Chassé
Arboretum de Chocha:
Arboretum de Chocha, France - Michel Duhart
Jardín Botánico de Iturraran
The Collection of Oak Trees of Mexico and Central America in Iturraran Botanical Gardens - Francsico Garin Garcia
1 Editor's note: Though the name Acer ×pseudoheldreichii is used by some references, including Trees and Shrubs Online and The Maple Society, it was not validly published. Fukarek and Celjo published the name in the journal Sumarstvo (November/December 1959 issue), but the article (in Serbo-Croatian with an abstract in French) did not include a description or diagnosis in Latin, a requirement for valid publication for names published between 1 January 1935 and 31 December 2011 (see Art. 39.1 of the Code). With thanks to Nikola Šušić for kindly providing a copy of the original publication.
