Abstract: To clarify the morphological differences of pollen among genera in the family Zygophyllaceae, we examined optical microscopic characteristics of pollen from six species, including Tribulus terrestrisL.,Nitraria tangutorum Bobr., Sarcozygium xanthoxylonBunge, Peganum harmala L., Tetraena mongolica Maxim., and Zygophyllum mucronatum Maxim. from western Inner Mongolia. Classification and regression tree (CART) analysis was performed on the quantified data of main pollen characteristics to explore the relationships between the classifications of pollen morphology and their taxonomic classification in ‘Flora of China’. The results showed that the grains of Zygophyllaceae pollen were mainly smallsized and spherical, subprolata, or prolate. The apertures of pollen were 3-colporate, 3-pseudocolporate, and pantoporate. The exine ornamentations of pollen were reticulate and striate. Most pollen grains had colpus membranes. The polar axis of Tetraena mongolica and Zygophyllum mucronatum was shorter, while the equatorial axis was longer than that reported in literature. The results of CART classification tree were quite different from the classification of ‘Flora of China’, suggesting that the pollen morphological characteristics, which are less evolved with environmental change, can be used as a potential proxy to reveal the phylogenetic relationship of plant species.

Key words: tree, biotic factor, abiotic factor, temporal scale, non-structural carbohydrate, spatial scale, Inner Mongolia, Zygophyllaceae, pollen morphology, CART classification tree.