Species Spotlight: Quercus rotundifolia Lam.

By Francisco Vázquez and Roderick Cameron. 
Originally published in Oak News & Notes, Vol. 19, No. 1

Quercus rotundifolia Lam. has a range restricted to the western-most quadrant of the Mediterranean basin. It is a rugged species that can survive temperatures below -20 °C, and can live in conditions with temperatures that on occasion reach 47 °C during summer months. It adapts to all types of soil: poor, rich, deep, skeletal, sandy, lime, clay, neutral, alkaline, and acid. In its natural habitat it is a rustic tree, with bark that varies from dark grey to ochre. The grey-blue canopy is umbrella-shaped, and the small to medium-sized leaves have entire margins or are slightly spiny and very tomentose. The tree flowers in spring and very frequently again in autumn, when temperatures become spring-like. An outstanding feature of this species is the connection it has had with  

A mature specimen of Quercus rotundifolia. Photo: ©Francisco Vázquez

humans. There is evidence that its fruit has been used for human nourishment since the Neolithic era (7,000 BC): the inhabitants of the southern Iberian Peninsula 9,000 years ago collected acorns of Q. rotundifolia in autumn (November), gently toasted them in order to preserve them throughout the year, ground them in manual granite mills, and ingested the flour in soups or breads.

This species is closely related to Q. ilex, and in Spanish they share the same common name: encina. There is disagreement amongst taxonomists, for although it is generally agreed that they are separate taxa, some consider them to be separate species, whereas others classify them with subspecies rank.

The acorns of Q. rotundifolia, which come in a wide variety of shapes and sizes, are used to fatten Iberian pigs and other domesticated animals. Eight different varietal forms have been named, based on differences in acorn morphology (for details and descriptions, see International Oaks No. 11, 2000, pp. 39-52). These forms, however, have not been accepted by Kew’s World Checklist of Selected Plant Families, where they are listed as synonyms. Amongst the varieties of acorns worthy of mention are Q. rotundifolia var. macrocarpa (Cout.) F.M. Vázquez, S. Ramos & S. García, with large acorns that can weigh up to 35 g (fresh weight) and Q. rotundifolia var. avellaniformis (Colmeiro & E.Boutelou) F.M. Vázquez, S. Ramos & S .García, with small acorns (resembling hazelnuts) that don’t exceed a fresh weight of 4 g.

Q. rotundifolia (left) vs. Q. rotundifolia var. macrocarpa (right) Q. rotundifolia var. crassicupulata vs. Q. rotundifolia var. macrocarpa

Encinas form an essential part of the forestry and livestock system known as dehesa in Spain and montado in Portugal, consisting of woodlands where the forest has been domesticated: most of the shrub-like elements have been removed to promote grasslands, and oaks have been cleared to improve soil illumination and herbaceous growth. Furthermore, the trees have been domesticated: the encinas have been pruned to form umbrella-shaped canopies, with principal branches parallel to the soil, of medium height (up to 8 m), and the inside of the canopy has been cleared to allow the access of sunlight, all to benefit fruit production. The encinas belong to a forestry system that has been intervened, which holds a cultural patrimony and preserves ancient traditions, and which has been adapted to human needs during each era of the last 10,000 years of mankind’s existence.

Q. rotundifolia var. avellaniformis
Photos: ©Francisco Vázquez 
Q. rotundifolia var. avellaniformis vs. Q. rotundifolia var. macrocarpa