Comparative pollen morphology of the genera Axyris L., Ceratocarpus L., Grayia Hook. & Arn. and Krascheninnikovia Gueldenst. (Amaranthaceae)

Based on morphological, morphometric and molecular data, Axyris , Ceratocarpus and Krascheninnikovia were classified to the subtribe Axyridinae, and later this group was elevated to tribe Axyrideae (Chenopodiaceae / Amaranthaceae). Previously, the representatives of these three genera, together with Grayia , have been included in the subtribe Eurotiinae. Their relationships are poorly understood; the position of Grayia still remains unclear. Considering that palynomorphological traits can be useful for angiosperm taxonomy, the aim of this research was to provide detailed data on the Axyrideae and Grayia pollen characters and to evaluate their taxonomic significance. Pollen morphology of 13 specimens belonging to seven species of the genera Axyris , Ceratocarpus , Grayia (including Zuckia ), and Krascheninnikovia was studied using light and scanning electron microscopy . Pollen grains are pantoporate, spheroidal, circular in outline, small or medium-sized. Exine sculpture and pore membranes are nanoechinate, tectum is psilate-perforate. The data obtained showed that species and genera can be identified based on palynomorphological features, especially the pollen diameter, pore number, pore diameter, distance between pores and between pore centres, nanoechini density, number of nanoechini on pore membranes, exine thickness, and structure of columellae. Exine structure (columellae) of pollen grains of all species was analysed for the first time in the present study. UPGMA dendrogram, based on quantitative pollen traits (nanoechini height, width at the base, number per 4 μm 2 , and number on pore membrane), supported the differentiation of genera. The data obtained confirm the close relationships between tribe Axyrideae ( Axyris , Ceratocarpus , Krascheninnikovia ) and Grayia (including Zuckia ). This study highlights the importance of palynomorphological characters for the taxonomy. • Pollen morphology of genera Axyris , Ceratocarpus , Grayia , and Krasheninnikovia (Amaranthaceae) was studied using LM and SEM. • Exine structure (columellae) of pollen grains of all species was analysed for the first time. • Important diagnostic features at species level for taxonomical purposes were established. • UPGMA dendrogram, based on quantitative pollen traits, supported the differentiation of genera. • Data obtained do support a close relationship between Grayia and the species of tribe Axyrideae.