Characteristics of heteroblasty in Hladnikia pastinacifolia (Apiaceae), a rare endemic from Slovenia

Hladnikia pastinacifolia, the most prominent endemic plant species in Slovenia, is rare and protected because it is a stenoendemic and paleoendemic species restricted to area of Trnovski gozd (W Slovenia). However, this species can be found in various habitats. The disparity between the nonspecific habitat preference of the species and its rarity has not been sufficiently explained. Here we focus on the functional morphological features that are most indicative for the ecology of plant species: the anatomical and morphological characteristics of leaves. Hladnikia pastinacifolia exhibits heterophylly during ontogeny (heteroblasty). We aimed to describe and compare the anatomical characteristics of three H. pastinacifolia leaf morphotypes among them and in relation to various habitats. Therefore, we compared leaf functional features that are indicative for the ecology of plant species: the thickness of the leaf lamina, the spongy and palisade parenchyma, the thickness of the upper and lower epidermis and the number of leaf stomata in the upper and lower epidermis. These measurements were further used to calculate the ratio between the spongy and palisade parenchyma, leaf stomata index and the density of leaf stomata. We determined that the H. pastinacifolia heteroblasty belongs to the Apium-type. Results showed that the five-pinnate leaves were the most distinct type, being the thickest, with the highest numbers of stomata abaxially. When compared among habitats, leaves from the scree habitat were the thickest according to all the tissue layers studied. The indices calculated were less useful for the distinction between leaf types and habitats