MORPHOLOGICAL AND ANATOMICAL COMPARISON OF MERICARPS FROM DIFFERENT TYPES OF UMBELS OF HERACLEUM SOSNOWSKYI

Sosnowsky’s hogweed (Heracleum sosnowskyi Manden.) mericarps were collected from satellite and stem branch umbels for comparative anatomical investigation. Located near Vilnius city, the habitat of Heracleum sosnowskyi, formerly a natural forest edge has recently been densely occupied by plants of this species. SEM micrographs of abaxial and adaxial surfaces of mericarps obtained from satellite and stem branch umbels of H. sosnowskyi were similar, but morphometrical analysis revealed statistically significant differences in mericarps collected from satellite umbels, which were longer and wider than mericarps from stem branch umbels. The data on longitudinal sections of H. sosnowskyi mericarps clearly showed that embryos of satellite umbels were at later torpedo stage compared to embryos of stem branch umbels, which were at earlier heart stage. These data represent unequal development of the embryos in mericarps from different types of umbels. Such different development can be treated as an adaptation of the invasive plant to occupy the current habitat and survive in the seed bank by allowing the embryo to complete development within a seed and germinate when new conditions permit.