XVI International Botanical Congess

Adventive part of modern city's flora is 48.9% in comparison with 31.2% century ago. The most group consists of weeds of American origin. They appeared by different ways and behavior of newcomers was various. Those plants include annual and perennial herbs, trees and shrubs. Some of them with different speed (30-100 years) became unificators of Odessa's urbanoflora (Acer negundo, Galinsoga parviflora, etc.). Others as Euphorbia dentata, Amaranthus palmeri, etc. may be considered as naturalized. Some species (Legusia, Amsinckia) were found in 1993-1995 and have been studied. Main source of their appearance was grain loads from different countries of the world. Only from USA every year appeared seeds of quarantine weeds near 30 species.