The objective of this study was to investigate involucre morphological variability of common hornbeam (Carpinus betulus L., Betulaceae) populations in Turkey. In total, 12 natural populations of common hornbeam located in four different watersheds of the Eastern Black Sea Region were sampled from three different altitude zones up to 1200 m a.s.l. Involucres have been examined biometrically by analyzing 13 morphological characteristics. High phenotypic variability was determined both among and within the studied populations. Furthermore, grouping of populations according to the eco-geographic principle was revealed. Variation in most of involucre characteristics from the Camlihemsin, Caykara and Trabzon-Macka watersheds appeared to be related mostly to altitude. The trees in the higher elevations were characterized with the smaller involucres than those in the lower elevations. However, this trend has not been observed in the populations from the Giresun-Espiye watershed. Moreover, trees from that region at lower altitude had the smallest involucres. Overall, our results confirm the Eastern Black see region as one of the hot spots of biodiversity and that the involucre morphological variability is the result of the complex evolutionary process related to the adaptation and plasticity.
