SYSTEMATIC STUDIES IN SOME IPOMOEA LINN. SPECIES USING POLLEN AND FLOWER MORPHOLOGY

The current study was conducted in search of constant morpho-anatomical characters to aid the identification and classification of commonly encountered Ipomoea species in south west Nigeria. Flower and pollen morphology as important repository of constant characters formed the focus of the investigation. Whole flowers were dissected to expose the carpel and stamens for study. For pollen study, after soaking in de-ionized water, the anthers were collected and crushed, stained and placed on a glass slide by needle for observation under light microscope. The lengths of styles and filament all varied in the seven species, highest length in styles was recorded in Ipomoea hederifolia (37.0-38.5mm) while the minimum was recorded in Ipomoea vagans (16.5-19.0mm). United bract into a boat-shaped, doubly acuminate involucre distinguished Ipomoea involucrata from the remaining six species with free bracts. Pollen grains were found to be radially symmetrical; circular in outline, sculpture were echinate, circular aperture, pores equidistantly distributed, oblate, speriodal and oblate-spheriodal. Largest pollen size was recorded in Ipomoea aquatica (60.2-62.5μm), suggesting a less derived position whereas the minimum size (30.7-31.4μm) was observed in Ipomoea hederifolia. The maximum spine length was recorded in Ipomoea involucrate (8.3-9.6μm) and minimum was recorded in Ipomoea hederifolia (3.3-4.0μm). The phylogenetic tree resulting from cluster analysis suggests that the alien species I. aserifolia and I. carnea are sisters to the other native Ipomoea species. As the number of species increases, synapomorphies decrease whereas increased synapomorphies are associated with decreasing number of species.While both I. aserifolia and I. carnea may have naturalized, they represent new records for the Flora of West Tropical Africa.