Study of 15 Varieties of Herbaceous Peony Pollen Submicroscopic Morphology and Phylogenetic Relationships

Paeonia lactiflora Pall. is widely used in medicine, garden applications, and as a potted ornamental. Cultivated varieties of paeonifloras suitable for cut flowers are urgently needed. In this study, the pollen morphology of P. lactiflora was studied and the characters of different varieties were compared, so as to provide reference for selecting suitable parents for new hybrid varieties. We examined the pollen morphology of 15 herbaceous peony varieties using scanning electron microscopy and analyzed the external pollen morphology and genetic relationship of the varieties. The pollen grains of the studied varieties were spheroidal or subspheroidal, bilaterally symmetrical monads, circular in polar view, and circular or elliptical in equatorial view. The exine of the pollen grains was observed as being relatively smooth under the light microscope, with the area around the equatorial axis having more lumina under the scanning electron microscope. The pollen grain exine sculpture was either reticular or pit type. The pollen apertures were tricolporate, arranged longitudinally, and equally spaced. The pollen grains were of two sizes: medium and small. The differences between the varieties were mainly reflected in the exine sculpture of the pollen. The closer the genetic relationship between the 15 peony varieties, the more subtle the differences in the exine sculpture. In the same cluster group, the morphological characteristics of herbaceous peony pollen were correlated with the shapes of flower and scale buds and the texture of the petals. However, the study identified no direct correlation with the cultivar type and flower color.