Pollen morphology of selected crop plants from southern China and testing pollen morphological data in an archaeobotanical study

Identification of pollen grains of cultivated plants is essential in archaeobotanical studies. In this study, we investigated the pollen morphology of 30 species which are representatives of most of the crop plants in southern China, using a light microscope. Our results show that the pollen grains of these species or genera can generally be identified by their size, aperture(s) and exine sculpture. We found that: (1) some cultivated cereals can be distinguished from wild species of Poaceae according to their size frequency combined with their morphological features; (2) the lengths of the equatorial diameter (E), polar axis (P) and the greatest dimension of the lumina (the size of the network sculpturing) of the exine reticulum may be diagnostic features to distinguish some brassicaceous vegetables. There are significant differences between the E and P values among Brassica campestris (B. rapa, oilseed rape, Chinese cabbage), B. alboglabra (B. oleracea var. alboglabra, gai lan, Chinese kale), B. parachinensis (B. rapa var. parachinensis, choy sum, Chinese flowering cabbage) and B. chinensis (B. rapa ssp. chinensis, pak choi), but moderate differences in the longer axis length of the reticulum lumina, which provide potential for identifying species on the basis of pollen grains. We compared the P values and the longer axis length of the lumina of modern specimens of Brassicaceae pollen grains with those of fossil pollen extracted from the Ming-Qing cultural layer in the Fuqikou site at Chongqing, China, and found that the fossil pollen grains of Brassicaceae probably represent vegetable plants related to B. parachinensis. Moreover, we measured the diameters of rice pollen grains from modern paddy fields to assess the pollen size frequency and found that the size range from ~ 34 to 38 µm is closely associated with rice pollen in southern China, which can be used to detect pollen signals of human activities in archaeobotanical investigations.