Abstract
The morphometric characteristics of the North American invasive plant Cyclachaena xanthiifolia (Nutt.) Fresen were studied in the Kostanay region, Kazakhstan. Monitoring of plant populations has been ongoing since 2021. Vegetation begins in the first decade of May, ends in the second or third decade of September, lasting 146 days. Flowering occurs in late July and is prolonged, classifying the species as a late-summer flowering plant with long flowering duration. Fruiting is rapid, starting in the third decade of July, continuing until the end of August. The phenological phases of bud formation, flowering, and fruiting overlap, flowering and seed ripening are uneven. Analysis of variation coefficients shows that the amplitude of variability of traits in C. xanthiifolia does not differ widely, encompassing only 2 levels of variation - normal and significant, with the majority of parameters having normal Cv (%) values in all three months. The maximum Cv value in the C. xanthiifolia population does not exceed 47.7% (number of leaves on lateral shoots in July), the minimum is 10.58% (number of leaves in August). Cyclachaena xanthiifolia is a highly competitive weed that rapidly spreads throughout the region, quickly occupying dominant positions in plant communities, displacing all other plant species.