Taxonomic importance of pollen morphology in Veratrum L. (Melanthiaceae) using microscopic techniques

Previous studies reported that intrageneric relationships of genus Veratrum of family Melanthiaceae are controversial and hard to delimit. Therefore, we observed the pollen morphological features of six species in the genus Veratrum in detail using both light microscopy and scanning electron microscopy and investigated their significance for Veratrum taxonomy. Among them, five were studied for the first time. The results demonstrated that pollen grains of Veratrum are medium in size with P/E being 0.31-0.60. Three types of shape in polar view have been observed elliptic, long-elliptic, or wide-elliptic with blunt or rounded at both ends. Two types of width of colpus reported narrow or wide, two types of depth of colpus reported deep or flat, and two types of length of colpus reported extend almost or do not extend to the ends, whereas two types of colpus membranes reported absent or obvious. One type of surface ornamentation was noted as reticulate. These results support species Veratrum album and Veratrum lobelianum as well as Veratrum grandiflorum and Veratrum oxysepalum as two independent species, respectively, rather than classifying Veratrum into two sections. Overall, we demonstrated that the ratio of polar axis length to equatorial axial length, pollen characteristics at the polar view, the colpus morphology, and the surface ornamentation of pollen grains of genus Veratrum have important systematic significance in identification and delimitation of species.