Although a few cases of natural occurring triploids have been mentioned in the literature (Butorina, 1993; Naujoks et al., 1995; Dzialuk et al., 2007), oaks are diploid species bearing 2n=24 chromosomes. Extra chromosome 2n=24+1,2 or 3 extra chromosomes have been reported as consequences of irregular segregation in mitoses (Zoldos et al., 1998). Reported karyotype studies in Quercus, Lithocarpus, Castanopsis and Castanea (Mehra et al. 1972), and in Quercus (D’Emerico et al. 1995), and Fagus (Ohri and Ahuja 1990, 1991) indicate that the number of chromosomes within the Fagaceae family as a whole is remarkably stable (2n=24).

The reported values of 2C DNA content between oak species vary from 1.17 pg (Q. velutina) to 2.00 pg (Q. coccifera and Q. suber). Species that were investigated include representatives of all three major sections (12 species in Erythrobalanus (red oaks), 12 species in Lepidobalanus (white oaks), 4 species in Cerris). The average 2C DNA contents were 1.81 pg for section Cerris, 1.75 pg for section Lepidobalanus, and 1.56 pg for section Erythrobalanus (Kremer et al., 2007, and table attached). The two oak species with largest genomes, Q. coccifera and Q. ilex (2.00 pg), are both evergreen species and are part of a disputed botanical group (subgenus named Sclerophyllodrys, according to Schwarz (1964)), but are in two different sections in Camus classification (Q. ilex in section lepidobablanus and Q. coccifera in section cerris). This is intriguing, given that molecular phylogenetic analysis separates the evergreen species from the two sections of deciduous oaks (Manos and Steele 1997 and Xu 2004) confirming their earlier subdivision in Sclerophyllodrys by Schwarz (1964).

2C DNA values in related genera are at the lower limits of the range of values observed in oaks: 1.62 pg for Castanea and 1.17 pg for Fagus




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