This paper is dedicated to some of the beliefs and customs of the ancient Slavic folk related to plants and animals. The aim of the study was to describe some species, which appeared in the selected myths and legends concerning Slavs. They usually represented two spheres of nature: real/rational and imaginary/irrational. Hence, the store of knowledge and ignorance that existed in those times was translated into a particular, often mythologized texts, some of which survived in the culture until this day. The rational side of nature was represented by agriculture, but also some medicinal and cosmetic plants. The other side was expressed by the fears and anxieties of people from those times, and was used for various purposes, such as witchcraft and love magic. In such tales, it is plants that usually make the central motifs, and animals are captured in the background, only accompanying them. Yet, the latter seem more mysterious and endowed with greater powers. In the middle of those spheres, there is located a theme of the tree, which is also known as a “space tree” or axis mundi, used for describing the universe. Due to the prevailing specific natural conditions, it is easy to imagine that such a motif was the most readable symbol of the world through which death and rebirth of nature were observed, standing somewhere between these spheres and penetrating the particular dimensions.