engleski

Pollen and seed Morphology of the genus Hypericum L. (Hypericaceae) - taxonomical implications

The large genus Hypericum L. (Hypericaceae) comprises about 470 species, grows all over the world, and is divided into 30 main sections and 6 additional subsections. Although its molecular phylogeny is well researched, taxonomic studies of other characters of the genus Hypericum are still on-going. The aim of our study was to investigate the possible taxonomical and evolutionary significance of micromorphology for the genus. Therefore, pollen and seeds of 32 taxa (from 14 sections) were studied by scanning electron microscopy. The results showed new features of pollen and seeds for 14 Hypericum species, some new irregularities of their pollen morphology, and some of our results are similar to previous studies. Pollen grains are regularly three- stephanocolporate with a microreticulate to reticulate ornamentation pattern. Some taxa showed irregularities. They can produce more than three apertures and hence loose its polarity. In spite of eleven distinct pollen types in a previous research, our results pointed to a smaller number of pollen types for the genus Hypericum. Seeds morphology showed the characteristic features of the exotesta sculpture, probably caused by the differences in the wall thickness of the cells of the outer layer. These are probably the most distinctive feature of Hypericum seeds that help to distinguish entire sections and show a general evolutionary trend of seed morphology from cylindrical to carinate and/or narrowly winged. Our SEM observations also showed some new exotesta sculptures. Different taxonomical implications of the researched micromorphological features, especially those which could be used for delimitation of some taxa of the genus Hypericum, will be briefly discussed.

Hypericum ; pollen ; seed ; taxonomy

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