A comparative analysis of invasive components in several regional floras within European Russia is carried out. Regional specifics of alien floral components, caused by climatic differences and local traditions in the cultivation are described. Trends of changes in the florogenetic and invasive statuses are revealed for number of alien species. Tasks for a program of integrated studies on the alien component of floras and for developing regional Black Books are formulated.

This paper represents a review of comprehensive research into invasion biology done by Russian scholars for four decades. Invasion biology is a relatively new field of research focused on the study of alien plants, their behavior in new habitats and risks they pose to indigenous species. It is shown that over 40 years, single finds of alien plant species have transformed into a check-list of invasive species in Russia. The most significant invasion pathways were identified, and the rate of microevolutional changes in plant species in their secondary distribution range was determined. Since the most active alien species disperse without regard to national borders, international cooperation is crucial in joint studies of invasive species.

A comparative analysis of Oenothera’s hybrid species was carried out. The genus Oenothera L. (subsect. Oenothera, Onagraceae) is one of the most widespread American genera in Europe. These species possess a special breeding system (permanent translocation heterozygosity) which promotes the hybridization (also introgressive one) among any species resulting in formation of a hybrid with a constant complex of morphological characteristics. The analysis of hybrid species distribution in Europe using published and original data proved the existence of groups with different degrees of invasiveness. A positive correlation between the degree of invasiveness of the parental species and the invasiveness of hybrid ones was shown. As a rule, the aggressive hybrids originated from aggressive parents. The most aggressive hybrids were formed after a crossing of North American with European species; perhaps such hybridization leads to the heterosis effect among normally isolated genes. The invasiveness of morphologically similar hybrids correlates both with their genetic features and with the abundance of the parental species. The new evolution branch of ring-forming species of Evening primroses is distinguished by high invasiveness in comparison with bivalent species. The invasiveness of the model species depends on plant cytotypes.

The complex of microspecies of the Bidens genus referred earlier to B. × garumnae is characterized. Generation F₁ does not inherit the prostrate habit and entire leaves, which are specific to parental plants, but each sample is uniform and has its own set of morphological and biological characteristics. In the studied locality, only one B. radiata × B. frondosa hybrid grows. No proof of the hybrid origin of other microspecies was found. It is proposed to perform the molecular genetic analysis of plant samples referred earlier to Bidens × garumnae and to describe them in the future as independent microspecies or intraspecific taxa.

A comparative study of the structure of the flower in three species of Robinia L., R. pseudoacacia, R. × ambigua, and R. neomexicana, was carried out. The widely naturalized R. pseudoacacia, as compared to the two other species, has the smallest sizes of flower organs at all stages of development. Qualitative traits that describe each phase of the flower development were identified. A set of microscopic morphological traits of the flower (both quantitative and qualitative) was analyzed. Additional taxonomic traits were identified: shape of anthers, size and shape of pollen grains, and the extent of pollen fertility.

It is shown that, in the invasion process, the G. orientalis phenotype has changed and differs from the natural one. The invasion phenotype is more “vigorous”: the total biomass of the top plant organs, the length of inflorescences, the number of flowers, and also seed productivity are increasing. A tendency toward augmentation of some morphometric features under the increase in duration of the naturalization process is noted. The study data reveal an increase in competitive ability of G. orientalis in the secondary range and support the EICA hypothesis (Evolution of Increased Competitive Ability).