So far, the allelopathy is relatively little studied for in vitro cultures. The present study aims to highlight the allelopathic interactions of in vitro cultures between two plant species cultivated on one hand for their economic importance, and on the other for their beauty, respectively Sequoia sempervirens (D. Don) Endl. and Stevia rebaudiana Bertoni; the research purpose was to determine the tolerability of one towards the other, in order to make in vitro floral arrangements, which are more and more popular and appreciated worldwide. Also, we plan to contribute in highlighting possible morphological and anatomical particularities of plants, which are in vitro co-culture, depending on the presence of growth regulators in the growing substrate. The analysis of this research revealed the existence of mutual allelopathy influence, synergistic from sequoia towards stevia, and antagonistic from stevia towards sequoia, the in vitro association being possible only until the age of 20 days of the in vitro cultures, up to which the allelopathy is mutually stimulating in the presence of 1 mg/l IBA. Keeping in vitro of both species in the same container of culture, over the age of 20 days, proved to be beneficial only for stevia plants, independently of the presence of growth stimulants.