Primary identifications and palynological observations of Perilla in China

Unresolved controversies concerning the classification of the monotypic genus Perilla L. have hindered the complete understanding and subsequent sustainable use of these vital food, oil, and medicinal plants to their full potential. In the present study, we used scanning electron microscopy to obtain palynological evidence from 21 samples of Perilla plants from seven provinces in China as a potential further attribute for classification. The findings showed that pollen grains from plants of 11 samples were oblate, whereas those of the other 10 were suboblate; there were no prolate pollen grains observed. Pollen grains from all samples had diverse exine ornamentations. Based on whether they had continuous tecta on the ornamentations, the pollen grains from the 21 samples were classified into two categories: (i) 14 with irregular reticulates; and (ii) seven with continuous tecta with no perforations. None of the samples was bireticulate. The ornamentation pattern and size of pollen grains jointly provided evidence that it is appropriate for use in classifying the genus Perilla into five varieties of one species. Furthermore, by comparison, it is concluded that the shapes and exine ornamentations of Perilla are unique among those of the seven genera already investigated in the subfamily Lamioideae. Using these pollen features, Perilla can be easily distinguished from the two other subtribes (Menthinae Brig. and Thyminae Brig.) in the same tribe, supporting the view that Perilla and the other four related genera can be classified into one subtribe (Perillinae).