There are 11 species of Portuguese oak trees, a new list states

For several decades it said that there are eight native Quercus in the Portuguese flora, but a new botanical list raises the number of these species of Portuguese oak trees to 11, the result of a long and complex research work led by Carlos Vila-Viçosa.

Quercus orocantabrica, Quercus estremadurensis, Quercus pseudococcifera and Quercus airensis are four names to retain from the “New annotated list of Portuguese oaks”. This fact was already acknowledged by the international botanical community and was published in a scientific journal published by the magazine “Mediterranean Botany”.

This review, which reinforces the importance of our country as a diversity hotspot for the Quercus species, is the result of work carried out by a team of Portuguese biologists, led by researcher Carlos Vila-Viçosa – working at CIBIO-InBio, at the Museum of Natural History and Science of the University of Porto and at Biopolis.

After several years of fieldwork, review of the scientific literature, analysis of botanical collections preserved in herbaria (in Portuguese and international museums) and, in particular cases, molecular studies (DNA), it was possible to identify unique characteristics of several species and seven hybrids among the already known species of the Quercus species.

“In the Quercus species it is very difficult to trace the boundary between species. These trees are very easy to hybridize and to exchange genetic information”, says the researcher, explaining that the crossing between similar species, which results in fertile descendants that cross again, makes it particularly difficult to tell the difference between species and hybrids, and to describe them from an ecological and biogeographic point of view (natural distribution areas, characteristics of these areas, from climate to soil, etc.).

This decoding made it possible to clarify uncertainties regarding taxonomy and nomenclature that, in some cases, persisted for more than a century. This is how the “new” species of Portuguese oaks were individualized:

– Two of them – Quercus orocantabrica and Quercus estremadurensis – fall under the general concept of pedunculated oaks (in which acorns are supported by visible peduncles) and Quercus orocantabrica replaces the common oak (Quercus robur). “We saw a large genetic divergence of the oaks from their European counterpart Quercus robur,” says the researcher. And the differences are so striking that it is possible to differentiate between the two species.

– The other two – Quercus pseudococcifera and Quercus airensis – are part of the group of kermes oaks and sheds a “new light” on Mediterranean arboreal kermes oaks, which have long been the subject of controversy in terms of taxonomy and nomenclature, in part given the similarities between several kermes oaks spotted West and East of the Mediterranean, and the several attempts to characterize, identify and name them.


6 data to retain about the “new” Portuguese oak trees

  1. The species that enter the new list of Portuguese oaks trees now have the following common names: Galician oak (Quercus orocantabrica2), common oak (Quercus estremadurensis), False kermes oak (Quercus pseudococcifera) and Serra de Aire Oak (Quercus airensis).​
  1. In the new list, seven species remain unchanged: Pyrenean oak (Quercus pyrenaica), Portuguese oak (Quercus faginea), Algerian oak (Quercus canariensis), oak or dwarf oak (Quercus lusitanica), cork oak (Quercus suber), holm oak (Quercus rotundifolia) and kermes oak (Quercus coccifera).
  2. The Galician oak is a deciduous tree that can reach more than 30 meters high. It differs by having, among other dissimilarities compared to Quercus robur, wider and brighter leaves, with a greater number of lobes and a longer petiole (the part that connects the leaf to the branch). It is naturally present in the Northwest of Portugal and Spain (the privileged area of distribution is the region of ancient Galicia), but is also distributed throughout the peninsular north, Serra de Sintra and São Mamede in Portugal.
  3. The common oak is a tree that can rise to 30 meters, from deciduous to marcescent leaves (in which the new leaves push the dead leaves). It is naturally present in the Iberian West, including in the Portuguese Estremadura and Spanish Extremadura provinces, as well as in southwest Alentejo and Algarve , with records in herbarium that point to its presence in the old days also in North Africa.
  4. The false kermes oak, previously considered a variant of the kermes oak, is a perennial leaf tree that can reach 18 meters high. Its trunk is smooth and grey and may gain fissures with age. The semi-hidden acorn is oval and narrow, and the dome has longer scales when compared to the kermes oak (Quercus coccifera). It lives naturally near the Portuguese Atlantic coast and in western Andalusia and North Africa, associated with the edges of the Portuguese oak and Monchique oak forests.
  5. The Serra de Aire kermes oak, once considered a hybrid between kermes oak and holm oak, tends to grow into a tree. Its leaves are usually covered by a layer of hair both at the top and bottom (called pubescent to tomentose leaves), which helps it reduce water losses and can justify its adaptation to soils derived from karst limestones, such as those found in the mountains of Serra de Aire and Candeeiros, Montejunto and also in Tetuan, Morocco.

5 hybrids of Portuguese oak trees new to science

In addition to increasing the number of Portuguese oak species from eight to eleven, the researchers also listed in the new list a total of 23 hybrids, five of them new to science:

  1. Quercus × almeidae (hybrid of pseudococcifera with Q. rotundifolia), named after the botanist Rubim Almeida;
  2. Quercus × alvesii ( lusitanica with Q. rotundifolia), whose name is dedicated to the botanist Paulo Alves;
  3. Quercus × capeloana ( pseudococcifera with Q. suber), which honors the botanist

Jorge Capelo (pictured below) .

  1. Quercus × eborense ( coccifera with Q. rotundifolia), named after the city of Évora, where Carlos Vila-Viçosa began focusing on the study of oak trees and where this hybrid is frequent, finding easily in arid areas and areas of Montado;
  2. Quercus × sampaioana ( estremadurensis with Q. lusitanica), in memory of the botanist Gonçalo António da Silva Ferreira Sampaio (1865-1937).

The new list also identifies the species grown in Portugal, in a total of 148 exotic oaks, “brought from other regions for their ornamental and economic value.” This identification was supported by Paulo Alves, who, like Jorge Capelo and Rubim Almeida, is part of the team that signs this scientific work, which also has Francisco Vázquez, a reference specialist in this genre at the Iberian and European level.


Unravelling the past of the Portuguese oak trees

Despite this clarification of names and species, other questions arise. For example, the existence in herbarium of records of Quercus estremadurensis from North Africa, from Tangier (where it may be extinct), suggests that the Iberian Southwest and Northwest Africa is an important area for the presence of a potential predecessor of the evolutionary lineage of European Quercus robur – constituting a relic species, which may have survived since the end of the Tertiary Period, more than 2.5 million years ago.

“They may have survived along with other relics still present in Southwest Alentejo and Algarve, such as the common rhododendron (Rhododendron ponticum) and the Monchique Algerian oak (Quercus canarienses)”, which are also being studied by a team that Carlos Vila-Viçosa integrates, within the scope of another project taking place in Serra de Monchique.

There is still much to know about Mediterranean and European oaks: understanding which species are related to the Portuguese and which can share the past with them, unveiling what the evolution of the Eurasia genus was, is one of the lines of research that Carlos Vila-Viçosa would like to pursue.

The origin and route of these species are unclear, so it is not known if they originated in the American continent and colonized Western Europe and later the areas to the East, or if the reverse happened and came from the East to the West. “There is an ancestral branch of Portuguese deciduous or marcescent oak trees that is probably American, but we do not know exactly how, after the arrival in Western Europe, the species evolved within this group and how they relate to each other,” he explains.

This knowledge can also help explain how oak trees have managed to resist or adapt to many of the environmental changes, including climate change, that have happened over millennia, information that may prove essential in defining better strategies for their current conservation.