Camellia sinensis (L.) O.Kuntze and most of its wild allies are used for tea throughout China and in many other parts of the world. Although they all belong to Camellia section Thea, their infrasectional classification remains controversial, resulting from heavy reliance on macromorphological features. Furthermore, the identification of tea from the fragments of processed leaves is quite difficult because of the lack of reliable characters. Here, foliar sclereids of 28 species and five varieties were investigated and used to explore their utility in addressing taxonomic problems and identification of commercial teas. Our data showed that foliar sclereids exhibit a wide diversity in this section. They could be divided into 12 types (including a newly recorded dendritic type) and two distribution patterns in the leaf blade. Their forms, type combinations and distribution patterns are reliable features, not particularly influenced by environmental factors, although their distribution density sometimes varies. In addition, they appear constant in individuals of different ages within the same wild population. We conclude that foliar sclereids in the section Thea are relatively stable and their diversity and regularity are of some taxonomic value.