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Plant Focus

Hybrid Highlight: the Langtry Oak

Adapted from an article originally published (in French) in issue no. 30 of  the Bulletin of the Association of French Botanic Parks (Association des Parcs Botaniques de France) in 2004, under the title "L’étonnante histoire d’un arbre oublié:‘le chêne de Langtry’" (The Amazing Story of a Forgotten Tree: ‘The Langtry Oak’).

This oak was originally described in 1858 by John Torrey as Quercus coccinea var. microcarpa, from samples collected by Charles Wright. During a mission led by Major Emory in charge of the topographic and linear survey of the borders of Texas, it had been observed growing on ridges of canyons, located just downstream from the confluence of the Rio Grande and the Pecos River (Emory 1859). Both of these rivers originate in the mountainous regions of northern New Mexico.

This description was known but it did not capture the attention of taxonomists. About a century later, the oak was again observed in situ, by Cornelius Muller, who considered it similar to Q. gravesii and the name Q. coccinea var. microcarpa Torrey became a synonym of Q. gravesii Sudworth (Muller 1940). So everything went back to normal… until the 1970s.

Syntype of Quercus coccinea var. microcarpa
Syntype of Quercus coccinea var. microcarpa, NYBG Steere Herbarium specimen no. 248624, collected by J.M. Bigelow

At that time, Benny J. Simpson,1 eminent Texan dendrologist, creator of a botanical garden, and excellent communicator through publications and television programs, and Lynn Lowrey, rediscovered this tree in nature. During his first collections of Pistacia texana, Lynn Lowrey had found this oak at Greenhouse Springs (also known as Hinojosa Springs), a locality which is at the level of a waterfall, near a ford on the Rio Grande; this place was already partially submerged by the creation of the Amistad Reservoir.

Both sides of the Rio Grande

It was through correspondence with Pat MacNeal, a nurseryman in Manchaca near Austin, Texas, that I became virtually acquainted with this strange oak, whose description frankly did not resemble a known species in this part of the United States.

In 1991, while surveying a private ranch near the town of Langtry, in southern Texas, this friend and member of the International Oak Society was able to harvest acorns and leaves from several subjects living in steep canyons, between 300 and 450 m altitude, on deep limestone and high pH.

According to the samples, it is indeed a Red Oak (section Lobatae); its leaves have morphological characteristics close to Mexican species like Q. canbyi or Q. cupreata and the Mexican/Texan Q. gravesii, of course, which is characterized by a great polymorphism linked to its different origins.

As Q. gravesii (and Q. buckleyi, another red oak) is found at close to 100 km from the populations of the oak he was trying to identify, Lynn Lowrey had thought that it could be a hybrid between Q. gravesii and Q. canbyi, which made sense to me when I first saw this oak tree.

Langtry oak at Arboretum de la Bergerette
Langtry oak at Arboretum de la Bergerette, France, spring 2020 © Shaun Haddock

But Q. canbyi is known today only in northeastern Mexico (Coahuila, Nuevo León and Tamaulipas) and normally does not exist or no longer exists in this southern sector of Texas (its supposed disappearance also possibly being linked to the construction of dams). We can assume without exaggeration that Q. canbyi could have sent to the other side of the Rio Grande a little of its pollen which, depending on the wind, would have fertilized specimens of Q. gravesii. Quercus canbyi particularly appreciates the bottoms of cool canyons and slopes and there may be a few examples of Q. canbyi left in these Texas canyons.

Pat MacNeal also thought this unknown oak might be related to Q. graciliformis, a phylogenetically and geographically close species (170 km to the west, in the Chisos Mountains), but the sinuses of the leaves of Q. graciliformis are much shallower and it is easy to distinguish.

It is worth noting that even when grown in the presence of Q. shumardii (as is the case at the Texas Discovery Gardens in Fair Park, Dallas, Texas, and at the Texas A&M AgriLife Research and Extension Center at Dallas ), the "Langtry oak" does not hybridize with that species because it flowers earlier.

In 1991, Pat brought the acorns home and sowed them (his nursery is located several kilometers north of the collection site and the climate there is essentially the same, except for the scarcer availability of water, which Pat supplements with appropriate watering). The young plants obtained show that "his" oak is very distinct from its companion trees, confirming his initial impression.

The first observation, and it is significant, is that this oak has perfectly evergreen (or sub-evergreen) foliage. In the first two field studies (by Torrey and Muller), the trees were not observed in dormancy; they had been considered deciduous, which corroborated the synonymy with Q. gravesii, itself deciduous (even if it sometimes retains part of its foliage at the start of a mild winter). However, none of the other morphologically similar species has completely persistent foliage, at least until the following spring. This characteristic is not accidental: it has been observed every year on all subjects sampled by Pat since 1991.

And that's not all: when cultivated, the descendants of the trees that have been collected in situ come true and are homogeneous. This suggests it is not hybrid but a species in its own right. Its distant origin is, on the other hand, perhaps hybrid?

Langtry oak at Pouyouleix
Langtry oak at Arboretum des Pouyouleix, France, August 2020 © Thierry Lamant

The theory that this oak is a species of hybrid origin remains plausible. Although the Langtry oak is the only Red Oak present in the sector studied, we know from experience that such hybrids do not necessarily exist in the vicinity of their parents (like Q. ×dysophylla which is sometimes found in isolated populations, distant from it parents, Q. crassifolia and Q. crassipes). To cite a concrete example in the same geographical area, this is also the case of Q. tardifolia, endemic to the Chisos of Texas, whose taxonomic status is unclear and which could result from hybridization between the Mexican/Texan Q. gravesii and Mexican Q. coahuilensis. However, Q. coahuilensis has so far never been observed in the Chisos. It is not known if it disappeared from this mountain or if its pollen came from further afield in Mexico or even if the origin of Q. tardifolia in the Chisos would come from acorns carried by corvids.

In this sector of southern Texas and northern Mexico (northern Coahuila), on both sides of the Rio Grande, there are deep and poorly known canyons. This territory is sparsely populated, especially in Mexico, and deserves an exploration campaign by the Mexican authorities. We should be able to find other botanical treasures in this wooded area.

Paradoxically, it is in the U.S. part that prospecting is tricky. The owner who had allowed Pat to explore the oak canyons is now deceased and it was impossible for him to return. If you don't have a permit to walk on his land, a Texas landowner has the right to empty his gun’s magazine the moment you enter his property. The numerous cartridge casings visible at the foot of Texas fences attest to this...

It is not known what became of the oaks observed in 1991. Pat thinks that numerous waterworks in this part of Texas have, most likely, wiped out a large quantity. When we look at a recent map of the region, we see that this entire sector has been greatly disturbed by the construction of dams, like the one that buried the first populations observed after the Second World War.

Langtry oak at Pouyouleix 2
Leaves on a Langtry oak at Arboretum des Pouyouleix, October 2019 © Thierry Lamant

Pat observed other trees in hard-to-reach areas at the edge of the Devils River watershed, about 30 km east of the Pecos River watershed. The surroundings of these gorges are quite arid and made up of dry hills and arroyos (water-carved gullies).

We are as yet ignorant of almost everything about its hardiness. Naturally, it is more in zone 8b or 9a (respectively an average minimum between -7°C to -10°C or between -4°C and -7°C). Quercus graciliformis is hardy in zone 7b (-12°C to -15°C) and lives in comparable conditions, except for the nature of the bedrock (volcanic instead of limestone). We are therefore tempted to affirm a comparable prognosis.

As regards cultivation of the "Langtry oak", we can say that it supports soils with pH up to 8.2, that it appreciates the freshness of the canyons of its natural habitat and must therefore not lack a supply of water. I think that alluvial or colluvial soils should be suitable for it and that it can tolerate acidic pH values. We also know that it tolerates strong sunlight well, thanks to the cuticle that protects its leaves.1

Description of ‘the Langtry oak’

Trees can reach 15 m in height and have evergreen foliage. Its bark is fissured and similar to Q. gravesii, in contrast to that of Q. buckleyi, which remains smooth and grey. It forms small irregular scales when it grows on a soil well supplied with water.

Mature bark
Mature bark © David Richardson

Twigs are reddish and emerging leaves have glandular hairs; they disappear quickly except on the reverse where fine tufts remain in the axils of the secondary veins. Buds are red with white hairs at the base.

The petiole is reddish, glabrous (or with a few rare hairs) and is 1 to 1.2 cm long.

Underisde leaves Iturraran
Fine tufts of glandular hairs remain in the axils of the secondary veins on the undersides of the leaves; Iturraran Botanical Garden, Spain © Francisco Garin

The leaf is elliptical-oval in shape with 5 to 7 pairs of rather deep sinus lobes, with 9 to 15 mucronate tips (observation based on a low number of leaves); base attenuated and asymmetrical. Upper side is green, glabrous, and shiny, underside dull green, midrib prominent below. Leaves up to 9.5 cm long and 5 cm wide, blade firm despite being thin. In cultivation in Dallas, the foliage changes color around mid-February, turning slightly orange.

Foliage
The glabrous, shiny upper surface of the leaves of the Langtry oak © David Richardson

The cupules are hemispherical or turbinate (the top extends towards the branch, which carries it like a kind of peduncle), 1 to 1.5 cm long by 0.8 to 1.4 cm wide, sessile or subsessile, with reddish-brown triangular scales, closely appressed and pubescent to glabrescent. The rim of the cupule is somewhat denticulate. Acorns ovoid to ellipsoid, striated and pubescent then glabrous, 1.6 to 2 cm long by 0.4 to 1.3 cm wide. They ripen in the second year.

Acorns
Langtry oak acorns © Michel Timacheff

As for the name of this oak… for now, it is still Quercus sp. Langtry oak or Pecos red oak, while we wait—who knows—to be able to officially pay homage to one of the stubborn Texans who helped to make it known!

Editor's Note: Though this is posted as a Hybrid Highlight, it is not certain that the Langtry oak is in fact a hybrid. More information regarding the identity of this oak may soon be available thanks to comparative sequence analysis being carried out on samples collected last year (Adam Black pers. comm.)

Acknowledgments

Pat MacNeal, David Richardson, Mike Meléndrez

References

Emory, W. H. 1859. Report on the United States and Mexican Boundary Survey, Made under the Direction of the Secretary of the Interior. Vol. 2 pt. 1: Botany. Washington: Cornelius Wendell.

Muller, C.H. 1940. Oaks of Trans-Pecos Texas. The American Midland Naturalist 24(3): 703–728.


1 See Oak News & Notes Vol. 15 no. 2 for David Richardson's article about Benny Simpson.

2 Editor's note: Since the time this article was written in 2004, this oak has been in cultivation in several collections and appears to be hardy to zone 8. Shaun Haddock (pers. comm.) reports that at Arboretum de la Bergerette in France, while spring frosts may occasionally disfigure the leaves of this oak, they do not destroy them.