Comparative study on pollen morphological characteristics of 35 ornamental plants in Viburnum

The plants of Viburnum in the family Viburnaceae have extremely high ornamental value in gardens. To a certain extent, the morphological characteristics of pollen can reflect the evolutionary processes and kinship relationships of plants, but there are very few studies reported on the pollen morphological characteristics of Viburnum species. With the continuous development of new species in the genus Viburnum, this study aims to clarify the pollen morphological characteristics of common species with high ornamental value. Using scanning electron microscopy, the pollen morphological characteristics of 35 common Viburnum species in gardens were observed, and their interspecific relationships were analyzed based on pollen morphology. The results show that the pollen size of the 35 Viburnum species belongs to small (10-25 μm) or medium (25-50 μm), and the morphology is nearly spherical or elongated spherical. Among them, the pollen size index (SI) of Viburnum keteleeri is the largest at 29.39 μm, and the SI value of snowball viburnum is the smallest at 17.59 μm. Thirty-four Viburnum species have three germination furrows, accounting for 97.14% of the total. The pollen exine ornamentation is mainly divided into three types: reticulate, verrucate, and papillate, with the reticulate pattern being the most complex and the highest in evolutionary degree. Thirty-one species have reticulate ornamentation, accounting for 88.6%. Cluster analysis can divide the 35 Viburnum species into four categories. Combined with correlation analysis, it is known that Viburnum cylindricum has the most distant kinship with the other 34 species in terms of pollen.