Comparative HPLC-PDA analyses of methanolic root extracts of the almost unstudied Chinese endemic species Stemona mairei, collected from nine locations throughout its natural habitat in northern Yunnan, led to the identification of the pyrrolo [1,2-alpha] azepine-type alkaloid protostemonine (1) as the main alkaloid and 3,4-dehydro-delta-tocopherol (9) as the main tocopherol derivative. Analysis of the five further Chinese Stemona species S. sessilifolia, S. japonica, S. parviflora and S. shandongensis, collected in adjacent locations, resulted in identification of eight Stemona alkaloids, with seven of them possibly derived from 1. Additionally, the presence of three tocopherols was confirmed co-chromatographically with authentic samples. From S. shandongensis, the alkaloids stemocochinin (7) and croomine (8) were isolated and their structures confirmed by NMR and MS analyses. Additionally, the quantitative content of protostemonine (1) and the tocopherols 9 and 10 present in extracts were assessed. Concerning the tocopherols, S. mairei differs by the occurrence of chromenol derivatives from the other species which accumulate both chromenol and chromanol derivatives. Furthermore, the root extracts of S. mairei exhibited nematicidal activities against Panagrellus redivivus. These results are briefly discussed in a biological and chemotaxonomic context, respectively.