Morphologic variation in northern marginal Juniperus oxycedrus L. subsp. oxycedrus populations in Istria

Marginal tree populations are believed to be more differentiated and host less variation than central tree populations. The aim of this study was to perform a detailed morphometric study of J. oxycedrus L. subsp. oxycedrus in northern marginal populations in order to establish its phenotypic variation and geographical differentiation and to examine the eventual presence of putative species J. deltoides in Istria. Morphologic variation was studied in 16 northern marginal populations in Istria. Nine morphological traits from a minimum of 50 leaves from each of 206 individuals and two morphological traits from 30 to 50 seed cones in each of 103 females were measured. Phenotypic variation in Istrian populations was high and of a similar magnitude to that found in the centre of the distribution area. Gender dimorphism in leaf morphology was detected, but the study failed to confirm its uniform distribution pattern. Significant and surprisingly high among-population differentiation (8–30%) was revealed. Average leaf shape in the study area is clearly “delta-shaped” characterised by a relatively wide leaf base. However, no significant differences in any of the studied traits were found between the marginal Istrian populations and the more central populations analysed in our earlier studies.