O.N. Kurdyukova*

Cyclachaena xanthiifolia is one of the expansive and dangerous weed plants in the Asteraceae family in Ukraine. We have identified Cyclachaena xanthiifolia in all ruderal, segetal, and natural plant communities, as well as in various growing areas, from overmoistened meadows and forests to xerophytic steppe lands. Cyclachaena xanthiifolia spreading in agrophytocenoses was reliably associated with twelve melons and gourds, vegetable, and tilled crops. Such connection was not discovered with winter and fodder crops.
Spacing of Cyclachaena xanthiifolia in ruderal phytocenoses was diffuse or clumped; spacing in agrophytocenoses was single or by separate spots; spacing in natural sites was sporadic or by individual plants at considerable distances from each other.
The highest frequency of Cyclachaena xanthiifolia occurrence was in ruderal areas: landfills, manure storage areas, along the roads, R=93-100%; a little less occurrence was on pastures, along the fields edges, along the embankments, streets, canals, shelterbelts, R=56-74%; insignificant occurrence was in plating of tilled, vegetable and spring grain crops, R=35-47%; and single plants occurrence was in plating of perennial grasses and winter crops.
The plants greatest density (80-120 pcs/m2) was in the Northern and Southern steppe zones; the lesser density (20-30 pcs/m2) was in the Forest steppe and Dry steppe zones; and the smallest density (4-8 pcs/m2) was in Polesie and mountainous areas.
In landfills, wastelands, manure storage areas, and livestock farms, the number of Cyclachaena xanthiifolia plants in the seedling stage reached 420-480 pcs/m2 and 60-110 pcs/m2 in the stage of seed maturity. Along the field roads, forest shelter belts, canals, streets, and hedges, the plants density was 260-340 and 20-90 pcs/m2, respectively.
The ability of Cyclachaena xanthiifolia to the ubiquitous intensive spreading, dissemination and naturalization was determined by the method of seed spreading. In Ukraine, it was characterized by both natural and anthropochorous ways of seeds spreading. The natural way (85%) was more pronounced on ruderal habitats, and the anthropochorous way (90%) was pronounced in the agrophytocenoses.

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