Abstract <p>The results of a long-term study (2006–2024) on the phenology of 25 species of herbaceous plants, represented by 33 accessions from natural populations in the Russian Far East (Primorye, Sakhalin, and the Southern Kurils), under conditions of the forest-steppe of Western Siberia (Novosibirsk) are presented. The study has revealed the features of seasonal rhythms for most of the accessions: spring growth is observed in the early to middle period (April–first decade of May) and the onset of flowering is timed to the summer period (June–mid-July), with a phenorhythmotype classified as spring–summer-green. Therefore, with respect to the primary rhythmic characteristics, the Far Eastern accessions correspond to herbaceous perennials of the regional flora. At the same time, the complete and regular seasonal cycle as an indicator of biological sustainability is observed in 16 accessions (48%), while the others are unstable or weakly stable under the new environmental conditions. Main patterns of phenological shifts have been established based on linear phenological trends: a delay in the dates of onset of vegetation (6–13 days/10 years) and an advance in the dates of vegetation end (6–16 days/10 years). We have also recorded a later date of onset for flowering (up to 6 days/10 years) and an earlier date of its end (3 days/10 years), as well as a significant reduction in the duration of all interphase periods. A significant intraspecific variability of phenological events has been demonstrated depending on the provenance of materials. The findings indicate an accelerated seasonal development of Far Eastern perennials during their adaptation to continental climate.</p>