[in Chinese with English abstract: ] Definitions of the word “diyi” (lichen) in Chinese were investigated, and ancient books appeared from 2100 BC till AD 1912 were consulted; The concept that “diyi” is a symbiont was first proposed in 1858 in the book titled “Zhi Wu Xue” (botany) compiled by Li Shan-Lan et al. Key words: ancient books, “diyi” (lichen), source.