Are Quercus calliprinos and Q. coccifera the Same or Distinct Species?

Several authors have classified the “holly oak”, "horny oak", or “kermes oak” in diverse ways, considering the variability of different morphological traits or even discrepancies in molecular analysis and geographical distribution.

The holly oak (Quercus coccifera L./Q. calliprinos (Webb) Holmboe) is the only evergreen oak present all over the Mediterranean basin. This oak is diploid (Tutin et al. 1993). The fossil data suggested the presence of the holly oak from the Oligocene period in several countries of southern Europe and southwest Asia, while its ancestor was named Q. mediterranea Ung. (Simeone et al. 2018).

This evergreen oak shows high polymorphism, and the exact geographic distribution of the populations is not easily defined. This diversity in the morphology is coupled with the unclear nomenclature (taxonomy) since some authors suggest that the holly or horny oak complex is split into two different species: Q. calliprinos Webb, which has an eastern distribution (in the Mediterranean basin), and Q. coccifera L., which has a more western distribution. Depending on the variability of different morphological traits of the heterogeneous plant material examined, botanists classified Q. calliprinos either as an independent species or a subspecies of Q. coccifera, or even as a synonym for it.

Yet several authors from the western side of the Mediterranean Basin like Paffetti and collaborators (2001) or Vázquez Pardo and allies (2018) acknowledge that Q. calliprinos could actually be classified as a distinct species, while most of their colleagues from the eastern Mediterranean unequivocally distinguish it as a species or subspecies (Zohary 1961, Mouterde 1966, Yilmaz et al. 2013, Al-Qaddi et al. 2017, Yilmaz et al. 2017, Stephan et al. 2018)

To begin with, Camus (1938) differentiated between the two taxa mainly through their different area of distribution across the Mediterranean region: Q. coccifera was confined to the west, Q. calliprinos to the eastern basin, while both could co-exist in the Balkans and Italian Peninsula. Another major difference is the taller height that can be reached by Q. calliprinos. Even though this oak is generally found as a shrub in coppices and “maquis” formations, it occasionally reaches 20 m in height when preserved. On the other hand, Q. coccifera type is mostly a low shrub, except in a few locations where individuals reaching up to 15 m high have been observed and described as Q. coccifera f. pseudococcifera (Desf.) Villar (Quézel and Médail 2003).

The Mediterranean arboreal kermes oaks are traditionally assigned to Q. calliprinos, a tree originally described from northwest Africa (Tétouan, Morocco) and from Lebanon. According to Vázquez-Pardo and allies (2018), the author, Webb (1838), extended this original concept and species to the Middle East (Lebanon), in a comment on a plant earlier identified as Q. pseudococcifera Desf. by Labillardière, who simply cited that he found it in Lebanon. This resulted in confusion in the taxonomy of both groups. In 2023, Vila-Viçosa and collaborators confirmed this difference between both taxa, since the oriental Q. calliprinos “has glabrous and oblong to lanceolate leaves, with few stellate and fused-stellate trichomes in the proximal half of the leaf-blade and midrib, with characteristically large and free cup scales”, while the leaves on the western Mediterranean plants are tomentose on both surfaces. They also recommended the name Q. calliprinos Webb should be preserved with a new type for the eastern Mediterranean evergreen arboreal oak in future nomenclatural works (Vila-Viçosa et al. 2023). 

Quercus calliprinos is far more polymorphic than Q. coccifera, but the scarcity of studies in the Levantine countries on the morphology of Q. calliprinos is mainly attributed to its uniqueness as an evergreen species in that region (Zohary 1966, Mouterde,1966, Stephan et al. 2018).

Vázquez-Pardo and collaborators returned to the initial descriptions made by Webb to discriminate between both taxa: “Q. calliprinos has mature leaves with a pubescent (“downy”) leaf blade on both sides, and Q. pseudococcifera has glabrous leaves, in addition, the bracts of the cupule are usually flat, while in Q. pseudococcifera the bracts have a wavy margin. In addition to these characters we must mention the leaf trichomes of Q. calliprinos are pedicellate, and the rays prostrate to patent, while the trichomes of Q. pseudococcifera, when they exist, are sessile and the rays are erect to patent.” Nonetheless, according to Webb, Q. pseudococcifera is more frequent in the eastern basin, while Q. calliprinos occurs in the western basin predominantly. This led to greater confusion since today the western populations are attributed to Q. coccifera and the eastern ones to Q. calliprinos.

Zohary (1961) relied on leaf size, the texture of leaf margins (see Figure 1), bud shape, the hairiness of female flowers, and cupule and acorn traits (Figures 2 and 3) to discriminate Q. calliprinos from Q. coccifera. He couldn’t rely on an exclusive trait but rather took the bulk of the measured traits to distinguish them. Mouterde (1966) summarized the differences between Q. calliprinos examined in the Levant countries and those of Q. coccifera in the western basin: the strong pubescence of the young shoots (Figure 4), the limited number of spines on the leaf margins (Figures 1 and 5), and mostly the large tree size compared to the shrubby formation of Q. coccifera (Figures 6 and 7). 

In Türkiye and Italy, where both taxa co-exist, researchers have concluded that they should be separated into distinct species. Yilmaz and collaborators (2017) were able to differentiate among the different evergreen oaks of Türkiye by measuring several leaf and cupule traits. They concluded that the southern populations of Q. coccifera differ from the other groups and suggested that they belong to Q. calliprinos found in the Levantine countries.

Gentile and Castaldo (1976) were the first to delineate the presence of Q. calliprinos in the western basin as relict populations in Sardinia, based on leaf anatomy and morphology, despite the difficulty in differentiating both taxa due to the similarities in leaf traits. They considered that leaf traits alone are difficult to discriminate among coccifera and calliprinos samples, and anatomical and micrometrical traits should be used to support such discrimination. These traits include the shape and pattern of trichomes, appendages that constitute an extension of the epidermal cells in plant leaves.

The genetic or molecular analysis of the DNA of chloroplasts from different samples around the Mediterranean basin conducted by Paffetti and co-authors in 2001 discriminated Q. calliprinos and Q. coccifera as two separate entities. Cyprus, Greece, and Türkiye have populations of Q. coccifera in the eastern basin, while only Sardinia has Q. calliprinos relict populations in the western basin, like those found in Haifa in Israel. Samples examined from the Italian peninsula and France proved to be also Q. coccifera. The same results were obtained by Yilmaz and collaborators in 2013 by using random amplified polymorphic DNA (RAPD) data to discriminate among the Q. coccifera, Q. ilex, and Q. aucheri in Türkiye. They also revealed that holly oak samples from southern Anatolia could be separated from Q. coccifera, as suggested later by Yilmaz and allies (2017).

Conversely, Toumi and Lumaret (2010) investigated the genetic and evolutionary history of both taxa. Their results showed that the Q. calliprinos samples were characterized by higher allelic intensity and a strong geographical genetic structure. By comparing with fossil records, the authors attributed the lack of geographical structure in Q. coccifera to the regression of holly oak in the western Mediterranean Basin during the glaciations and a fast westward post-glacial expansion of Q. coccifera populations from the eastern Basin. The authors suggested that the two morphotypes are closely related genetically and constitute two components of the same species.

A recent study in 2020 conducted by Douaihy and collaborators on the genetic variability of oaks in Lebanon suggested that samples of Q. calliprinos from Lebanon hold an important genetic variability and belong to the West Asian-Eastern Mediterranean lineage as described by Simeone and coworkers in 2018. The results confirmed that the Middle East was both a shelter and a diversification center for species of this lineage.

From an ecological niche perspective, Mouterde (1966) distinguished Q. calliprinos from its vicariant Q. coccifera, through the following statement: “Obviously adapted to climates with at least a few months of aridity, this tree, undoubtedly incapable of supporting the rainy summers of oceanic Europe, is, for our regions, of remarkable vitality, allowing it to paradoxically survive in the most overgrazed or deforested places, and of great plasticity to endure all the climates of the Orient where a tree can grow. The only representative of the genus, it is at home near the sea, reaching up to 1600 m or more on the slopes of Lebanon, [and] infiltrates into Anti-Lebanon . . . It only stops on the road to Damascus when the conditions of steppe vegetation begin. It reaches this same desert limit at Jebel Druze”. These limits of distribution and this plasticity were later confirmed through ecological niche modelling conducted by Al-Qaddi and allies (2017), and Stephan and allies (2016 and 2020).

To resume, Q. calliprinos is distinguished from Q. coccifera by its oriental distribution along the Mediterranean basin, since it is found across the Levantine countries, Cyprus, southern Anatolia, Western Libya, Albania, Greece, and only in Sardinia-Italy in the Western Basin. Quercus coccifera is found in The Iberian Peninsula, Morocco, Algeria, Tunisia, Italy, France, the Balkans, Western and Northern Anatolia, and Cyprus. Such distribution could be also linked to divergent adaptation to environmental traits.

Another way to discriminate them is the size of Q. calliprinos, which is clearly taller than Q. coccifera. The leaf traits are not enough to discriminate those polymorphic trees from each other unless trichome anatomy and measurements are considered. The cupule and acorn traits were also supportive in discriminating both groups. Molecular analysis discriminated between both groups as well.

Hence, the consideration of either one single species with two subspecies or two separate species is more widely acceptable than a synonym from a taxonomic perspective. Since such differences occur at the morphological, molecular, and ecological niche levels, it is advisable to have both groups as separate species.

Works cited

Al-Qaddi, N., Vessella, F., Stephan, J., Al-Eisawi, D., and Schirone, B. 2017. Current and future suitability areas of kermes oak (Quercus coccifera L.) in the Levant under climate change. Regional Environmental Change 17, 143–156.

Camus, A. 1938. Les chênes, monographie du genre Quercus, vol 3. Lechevallier, Paris

Douaihy, B., Saliba, C., Stephan, J., Simeone, M. C., Cardoni, S., Farhat, P., and Bou Dagher Kharrat, M. 2020. Tracking diversity and evolutionary pathways of Lebanese oak taxa through plastome analyses. Botany Letters 167(3), 315–330.

Gentile, S., and Gastaldo, P. 1976. «Quercus calliprinos» Webb e «Quercus coccifera» L.: Ricerche sull'anatomia fogliare e valutazioni tassonomiche e corologiche. Plant Biosystem 110(1-2): 89–115.

Mouterde P. 1966. Nouvelle Flore du Liban et de la Syrie. Tome 1. Librairie Orientale, Beyrouth.

Paffetti, D., Vettori, C., and Giannini, R. 2001. Relict populations of Quercus calliprinos Webb on Sardinia island identified by chloroplast DNA sequences. Forest Genetics 8(1) : 1–11.

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Stephan, J. M., Teeny, P. W., Vessella, F., and Schirone, B. 2018. Oak morphological traits: Between taxa and environmental variability. Flora 243: 32–44.

Stephan, J., Chayban, L., & Vessella, F. 2016. Abiotic factors affecting the distribution of oaks in Lebanon.Turkish Journal of Botany 40(6): 595–609.

Stephan, J., Bercachy, C., Bechara, J., Charbel, E., and López-Tirado, J. 2020. Local ecological niche modelling to provide suitability maps for 27 forest tree species in edge conditions. iForest-Biogeosciences and Forestry 13(3): 230–237.

Toumi, L., and Lumaret, R. 2010. Genetic variation and evolutionary history of holly oak: a circum-Mediterranean species-complex [Quercus coccifera L./Q. calliprinos (Webb) Holmboe, Fagaceae]. Plant Systematics and Evolution 290(1): 159–171.

Tutin, T. G., Burges, N. A., Chater, A. O., Edmondson, J. R., Heywood, V. H., Moore, D. M., Valentine, D. H., Walters, S. M., and Webb, D. A., 1993. Flora Europea: Volume 1. 2nd Edition, Cambridge University Press, UK.

Webb, P.B. 1838. Iter Hispaniense. Paris : Béthune and Plon

Vázquez-Pardo, F. M., Coombes, A., Alonso, D. G., García, F. M., Meireles, C. R., Barrena, M. J. G., & Viçosa, C. V. 2018. Anotaciones a la nomenclatura del género Quercus L.,(FAGACEAE) en la Península Ibérica y NW de África. Folia Botánica Extremadurensis (12): 5–79.

Vila-Viçosa, C., Capelo, J., Alves, P., Almeida, R., & Vázquez, F. M. 2023. New annotated checklist of the Portuguese oaks (Quercus, Fagaceae). Mediterranean Botany 44: e79286.

Yılmaz, A., Uslu, E., & Babaç, M. T. 2013. Molecular diversity among Turkish oaks (Quercus) using random amplified polymorphic DNA (RAPD) analysis. African Journal of Biotechnology 12(45): 6358–6365.

Yılmaz, A., Uslu, E., & Babaç, M. T. 2017. Morphological variability of evergreen oaks (Quercus) in Turkey. Bangladesh Journal of Plant Taxonomy 24(1): 39–47.

Zohary, M. 1961. On the Oak species of the Middle East. Bulletin of the Research Council of Israel 4: 161–86.

Zohary, M. 1966. Flora Palaestina. Jerusalem Academic Press. Israel.

Photos © Jean Stephan