LEAF ANATOMICAL STUDIES OF THE GENUS HIERACIUM (ASTERACEAE) IN IRAN AND ITS TAXONOMIC IMPLICATION

Leaf anatomy of 17 taxa of the genus Hieracium belonging to two subgenera and six sections was examined using light microscopy in order to evaluate its systematic important. The studied anatomical characteristics show considerable variability among different species but are constant among different populations of one species. 28 characters were examined and among them, some characters have taxonomic value and can be used in delimitation of subgenera, sections, subsections and species. The most important characters are: presence or absence of lateral vascular bundles; main midrib shape; the thickness of epidermis, parenchyma, collenchyma and cuticle; the length of vascular bundles, xylem and phloem; lamina symmetry; the number of lateral vascular bundles and in few cases stomata size, the shape of epidermal cells and anticlinal walls. Moreover, an identification key to leaf anatomy of the species of Hieracium in Iran is given.