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Although the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. We evaluated the scaling of morphological, tissue-surface and vascular traits with overall leaf area, and the functional significance of such scaling. We examined 1,271 leaves for morphological traits, and 124 leaves for anatomical and hydraulic traits, from 38 trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4 m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We measured (i) tissue fractions within petioles and their second moment of area, (ii) theoretical xylem hydraulic efficiency of petioles and (iii) the extent of leaf vessel widening within the hydraulic path. We found that different scaling of morphological trait variability allows for optimisation of lamina display among larger leaves, especially the positive allometric relationship between lamina area and petiole cross-sectional area. Increasing the fraction of pith is a key factor that increases the geometrical effect of supportive tissues on mechanical rigidity and thereby increases carbon-use efficiency. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which also results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models. Leaf size variability modifies scaling of leaf traits in this large-leaved species.

The anatomy and micromorphology of the vegetative organs and calyx of Stachys scardica (Griseb.) Hayek were investigated using light (LM) and scanning electron microscopy (SEM). The analysis of the anatomical structure of stem, leaf and leaf petiole showed the presence of an additional adaxial phloem in the vascular bundle of the petiole that was recorded exclusively in species belonging to the subgenus Betonica. On the surface of studied plant parts, three types of trichomes were found: simple nonglandular uniseriate multicellular, nonglandular branched elongated and glandular peltate trichomes. The present study shows that certain micromorphological and anatomical features of Stachys taxa are valuable taxonomic characters. [Projekat Ministarstva nauke Republike Srbije, br. 173029]

We studied the anatomy of a rare narrow endemic species belonging to the Slovenian flora - Hladnikia pastinacifolia Rchb. Hladnikia is a monotypic genus with distinct taxonomic position within the Apiaceae family. The anatomical characteristics revealed by light and fluorescence microscopy provided new insights regarding the pollen, leaf and root characteristics of H. pastinacifolia, improving the understanding of its biology and ecology. Pollination, drought tolerance, life cycle and unattractiveness to herbivores explain the species’ persistence in time. Autofluorescence localized bioactive substances within secretory ducts and oil ducts.

Hardwickia mopane (mopane) leaves collected in the Northern Province (South Africa), Zimbabwe, Botswana, Malawi and Namibia have been used in a comparative study of leaflet and petiole anatomy. Morphological and anatomical features of leaflets and petioles collected from dwarf mopane and woodland mopane in the Messina area, South Africa was also compared. The material represents a wide range of habitats, environmental conditions and growth forms. For the anatomical investigations, use was made of cleared leaves, resin sections, light microscopy and scanning electron microscopy Features such as leaf movement, bundle sheath anatomy, presence of epidermal mucilage cells, stress metabolites and terpenoids are related to drought stress and predation. It is concluded that leaf and petiole anatomy is genetically determined and not influenced by short term environmental factors such as precipitation. Morphological changes of leaves formed during a growing season are highlighted.