Attempts have been made by linguists and anthropologists to reconstruct aspects of culture history by using synchronically derived lexical data. Related to this concern with culture history is one which attempts to explore the diachronic processes of lexical change over time. As a result of a comparative survey of Tzeltal and Tzotzil ethnobotanical knowledge, this paper presents evidence which demonstrates a positive correlation between lexical retention of plant names and the cultural significance of plant segregates to which plant names refer. While the present study is restricted to the semantic domain of ethnobotany of two languages, it is suggested that the principles at work are general to the ethnobiological lexicon of all languages. (Author/CLK)