The presented research investigated the pollen morphology of endemic Iraqi Hypericum species. The study revealed phenotypic features of pollen grains in the polar and equatorial views and their quantitative and qualitative characteristics. The results showed that the pollen grains of the genus Hypericum were radially symmetrical and isopolar, and their apertures were simple and tricolporate, except the species H. davisii, distinguished as tetracolprate. Dividing the studied species based on pollen grain sizes comprised two groups. Small pollen grains with an average length of the equatorial view ranged between 10–16 μm in H. lysimachioides and H. vermiculare. Medium-sized pollen grains with an average extent between 17–26 μm emerged in the species, i.e., H. retusum, H. triquetrifolium, H. perforatum, H. lydium, H. tetrapterum, H. asperulium, H. scabrum, and H. davisii. Pollen grains, also divided according to the P/E ratio, had two main groups. The pollen grains were subprolate and spherical, with the exine sculpturing examined by a scanning electron microscope (SEM), and isolated into four groups: 1) microreticulate reticulum, including H. asperulium, H. lydium, and H. vermiculare, 2) perforate, i.e., H. retusum, H. scabrum, H. tetrapterum, and H. triquetrifolium, 3) psilate with H. perforatum and H. davisii, 4) and reticulate exine sculpturing in H. lysimachioides, all isolated from the rest of the species. SEM images showed the thickness of exine ranged from 0.5 to 2 μm. The topical study also added H. davisii as a new species with no previous records in Iraq. This pollen study added valuable data for taxonomy and suggested that it should proceed with its first-time registration in Iraq. The pertinent research could provide a taxonomical key for Hypericum species in Iraq.

Keywords: Hypericum L., Hypericaceae, endemic Iraqi species, palynological diversity, pollen grains, SEM

Key findings: A comparative palynological study for the endemic Iraqi Hypericum species by light microscopy (LM) and scanning electron microscopy (SEM) determined the shape and size of the pollen grains, which were subprolate and sph prolate with small and medium size. Additionally, the ornamentation on the exine were microreticulate, perforate, psilate, and reticulate. The thickness of the exine was 0.5–2 μm. The number and shapes of apertures provide useful taxonomic information to distinguish the species. H. davisii was a new addition, having no previous records in Iraq.