The article is devoted to the study of the word-formation system of phytonyms and the ways of its description in the language of the Ala-Bulkun olonkho. Despite the importance of studying the names of the plants, the issue of phytonymic vocabulary of the Yakut language has not yet been the subject of a special study. The article was aimed at identifying the ways of interpreting the phytonyms in the olonkho language, as well as identifying the features of its description. As the material of the study served the nominations denoting the names of plants in the Yakut language collected from the text of the Ala-Bulkun olonkho. The descriptive method was applied and elements of the morphological analysis of the nominations were used in the study. Also, the lexemes were classified into lexical-semantic groups. The analysis of phytonyms nominations in the olonkho text revealed the features of the Yakut national culture. As well as various stable language formulas inherent in the Yakut language were identified, for example, kuekh ot ‘a green grass’, kuekh kharyia ‘a green spruce’, tengke mas ‘a tall tree’, tengke tiit ‘a tall larch’, uolakh mas ‘young medium-sized tree’, uolakh tiit ‘young medium-sized larch’, khatyng mas ‘a birch tree’. 8 nominations of phytonyms of plants in the Yakut language were revealed. The total number of references to nominations with phytonyms in the text of the epic work is 83, i.e. about a tree (28), larch (25), spruce (12), grass (5), birch (3), pine (1) and horsetail (1). Timofei Vasilievich Zakharov – Cheebiy described the names of the plants in the olonkho text with neutral, positive and negative connotations depending on the context. In addition to the above, we also studied phytonyms with various linguistic and stylistic motivations.