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ŠUMARSKI LIST 5-6/2018 str. 34     <-- 34 -->        PDF

1975), hybridization in oaks has greatly contributed to their extremely high variation and plasticity; it constitutes an important mechanism of their dispersal and is suggested to play a crucial role in their adaptive potential to changing climate (Rushton, 1993; Petit et. al., 2004; Aitken et. al., 2008).
Our case study focused on resolving the taxonomic status of a specific semi-evergreen oak tree described and known in literature as the “green oak” due to persistence of its thick green leaves deep into the winter (up to end of February). This individual tree grows in the village of Islam Latinski (Zadar County), Northern Dalmatia, Croatia, and has been protected as a nature monument since 1957 (HTRS96 x: 414861.9036, y: 4895526.4636) (Figure 1). It is estimated to be more than 200 years old (Borzan et. al., 1997). To the best of our knowledge, the first literature mention of the “green oak“ was by Jedlowski (1955) who presumed that the individual is a probable hybrid between Q. cerris L. and Q. suber L. Later, Trinajstić (1974a) described this particular individual tree as a hybrid Quercus × viridis Trinajstić, hybr. nov. suggesting that it is in fact a hybrid probably between Quercus cerris f. austriaca and Q. ilex (Figure 2). He based his description on morphological characters and the fact that Q. suber is not growing in the surrounding area. Afterwards, the peculiar green oak has been investigated several times including botanical, biological, taxonomical, detailed morphological as well as wood and leaf anatomy points of view (Siegert, 1995; Vranković and Pernar, 1995; Borzan et. al., 1997; Borzan and Pfeifhofer, 1998; Borzan, 2000; Guttenberger, 2000; Borzan and Stabentheiner, 2002). For example, Borzan (2000) has reported hermaphroditic unseasonal flowering in the green oak which lead to the detailed study of pollen and leaf hairs morphology of this individual compared to the putative ancestors Q. cerris and Q. ilex by scanning electron microscopy (Borzan and Stabentheiner, 2002). The latter study implied that the green oak does not share any similarities with Q. ilex based on these traits. Likewise, Guttenberger (2000) who has also performed measurements of the DNA content of the green oak and related oak species concluded that Q. ilex does not seem to be one of the parental species of the green oak.
Finally, the latest review on the origin of this particular oak by Muller et. al. (2003) suggested that this individual shares much more similarities with Q. cerris compared to Q. ilex; the authors conclude that all gathered studies of this taxon support the opinion given by Jedlovski (1955) and not the description by Trinajstić (1974a). However, the origin of this intriguing taxon remains still uncertain to date, and all