Lusitanian Oak

The Lusitanian oak or gall oak is the smallest of the Portuguese oak trees and one of the species that was first identified in Portugal.

The Lusitanian oak, also known as the gall oak, is the smallest of the Portuguese oak trees. Its scientific name Quercus lusitanica helps to identify it as a native species in Portugal and this is one of only three countries in the world where it exists naturally. The others are Spain and Morocco.

The Lusitanian oak is a small, irregularly shaped shrub that usually grows to a height of about 30 centimetres, but it can grow much taller, although it rarely exceeds three metres. Despite being creeper trees, they can spread over vast areas, since in some places their stems develop roots that give rise to new plants identical to the “mother plant” (the stems are thus called “stolons”).

Its bark is smooth and grey-white or brown in colour, and its branches are often covered with a thin furry layer (pubescent branches). Only one leaf (alternate leaves) grows from each node on the branches. Darker green in colour with a smoother surface on the upper side, the leaves are relatively thick, oval in shape and broadly toothed or serrated in the upper half or two thirds. The leaves remain attached even when dry and remain that way throughout the entire cold season, until they are ‘pushed off’ by new foliage the following spring (marcescent leaves).

The Lusitanian oak is a shrub with yellow flowers, or rather, with inflorescences that resemble clusters (catkins) and, as with all oaks, its fruits are acorns (glans) that hold the seeds inside. Lusitanian oak acorns are large and highly elongated, with a wrinkled cupule.

Even though the species exists only in the Iberian Peninsula and northern Morocco (where it is endemic) and despite the fact that the oak population is in decline, its threat status was considered to be of “Least Concern”. As set out in the Natura 2000 Sectoral Plan, the importance of preserving it is evident, since it was chosen as the dominant species in Habitat 5330pt4 – Mediterranean pre-desert scrubland, subtype scrubland with Quercus lusitanica.

Did you know that…

• The Lusitanian oak species was first identified in Portugal, which is why it was given the scientific name lusitanica. This was in reference to Lusitania, an ancient Roman province, which corresponds to a large part of what is now known as Portugal.
• Besides Lusitanian oaks, there are several other native types of oak trees in Portugal, such as English oaks (Quercus robur), Pyrenean oaks (Quercus pyrenaica), Portuguese oaks (Quercus faginea), Algerian oaks (Quercus canariensis), holm oaks (Q. rotundifolia), cork oaks (Quercus suber), and Kermes oaks (Q. coccifera). Among the many exotic species that can be found, the northern red oak (Quercus rubra) and the scarlet oak (Quercus coccinea), which both originated in North America, stand out.
• Just like our skin swells up when we get bitten by mosquitoes, when Lusitanian oak tree leaves get bitten by insects (of the species Cynips quercusfolii) when laying their eggs, cell multiplication occurs at a higher rate than normal and growths known as oak apples are formed. These rounded bulges are rich in tannins and were once used in the tanning industry, for manufacturing inks and dyes (for the dyeing of textiles and for writing), and for medicinal purposes. They are also known as galls and can be induced by the attack of various organisms to which different oak trees and various other species, such as the sweet chestnut tree (Castanea sativa), are susceptible.
• In the past, the branches of oak trees were used, along with other different types of bushes, to make bedding for livestock. Although little used as an ornamental species at present, it can be added to the shrub cover in parks and gardens, not only because of its beauty, but also because it requires little maintenance.

How do we protect Lusitanian oak trees?

Lusitanian oaks grow naturally on several estates owned by The Navigator Company in the centre and south of Portugal. It has been observed north of the Tagus, for example in Vila de Rei, but more frequently in the south: in Espirra, in the area around Monchique (such as in Corga Funda and Vale Tejoso), and also in the Odemira area (Southwest Alentejo), like in Vale de Beja and Amarelo. In some of these estates there are also areas that have been identified, classified, and mapped in accordance with habitat 5330 (Quercus lusitanica scrubland) as mentioned above.

At Quinta de São Francisco, it is also possible to find several examples of this species, especially in the southern part of this estate surrounded by century-old eucalyptus trees. Two specimens in particular are worthy of mention, one of which is located in the south-eastern part of the estate, nestled among some large Eucalyptus pulchella specimens, and the other in the south-western part, among several Eucalyptus elata specimens.

The known Lusitanian oak specimens are protected through selective measures, which preserve them during felling, deforestation, or the reduction of combustible biomass. The propagation of the species by means of acorns has also been considered at Quinta de São Francisco as a way of increasing the density of shrub cover and to shade areas where there are invasive species, such as acacias, for example.