Palynological features and taxonomic significance for 16 species of Gagea (Liliaceae) from Xinjiang, China

Since pollen characters can be used to help distinguish species, our aim was to determine if palynological information has taxonomic significance for Gagea species from Xinjiang, China. Gagea is widely distributed in north temperate and the subtropical zones. The genus has limited taxonomic characteristics and large morphological variation, which results in difficulty of species classification. Pollen morphology of 16 species of this genus was examined comprehensively via light microscope (LM) and scanning electron microscope (SEM). One qualitative and nine quantitative traits of the pollen grains were surveyed, followed by hierarchical cluster analysis (HCA). The pollen grains were bilaterally symmetrical heteropolar monads with a mono-sulcus and they were oblate or peroblate (Polar diameter (P) / Equatorial diameter (E) = 0.36–0.73) in shape and medium to large (P = 17.17–34.64 μm, E = 27.63–81.65 μm) in size. Three types of exine ornamentation were observed: perforate, microreticulate and reticulate cristatum. The HCA divided the 16 species into two groups. This research provides new data on pollen morphology for Gagea (the pollen morphology of eight species was reported for the first time). Pollen morphology also can be used to identify species with similar external morphology, such as G.nigra and G.filiformis. Furthermore, the study of pollen morphology not only provides new data for palynology research on Gagea, but also provides a basis for future classification of this genus.