Autopolyploidization has driven the successful invasion of Solidago canadensis in East Asia. However, it was believed that only diploid S. canadensis invaded Europe, whereas polyploids never did. Here, molecular identification, ploidy level, and morphological traits of ten S. canadensis populations collected in Europe were compared with previously identified S. canadensis populations from other continents and S. altissima populations. Furthermore, the ploidy-driven geographical differentiation pattern of S. canadensis in different continents was investigated. All ten European populations were identified as S. canadensis with five diploid and five hexaploid populations. Significant differences in morphological traits existed among diploids and polyploids (tetraploids and hexaploids), rather than between polyploids from different introduced ranges and between S. altissima and polyploidy S. canadensis. The invasive hexaploids and diploids had few differences in latitudinal distributions in Europe, which was similar to the native range but different from a distinct climate-niche differentiation in Asia. This may be attributed to the bigger difference in climate between Asia and Europe and North America. The morphological and molecular evidences proved the invasion of polyploid S. canadensis in Europe and suggest that S. altissima may be merged into a complex of S. canadensis species. Our study may be concluded that geographical and ecological niche differentiation of an invasive plant driven by ploidy depends on the degree of difference in the environmental factors between the introduced and native range, which provides new insight into the invasive mechanism.

Solidago canadensis L., native to North America, has become a troublesome invasive plant worldwide due to its strong sexual reproductive capacity. Although there have been studies on some stages of sexual reproduction, there has been no systematic description of the process. In this study, we observed capitulum development, the occurrence of megasporogenesis and microsporogenesis, and embryo development using a scanning electron microscope. The results showed that there was a close relationship between the length of the capitulum bud and the stage in the reproductive process. Capitulum development appeared when the length of the capitate inflorescence was less than 1.73 ± 0.08 mm. The meiosis of microspores occurred when the length of the capitate inflorescence ranged from 2.20 ± 0.07 mm to 3.50 ± 0.10 mm, and mature pollen grains and embryo sacs formed when the length of the capitate inflorescence was greater than 5.15 ± 0.14 mm. Based on the available information, a reproductive calendar showing the key reproductive events from capitulum development to seed formation has been prepared. These processes may be related to its inherent temperature adaptation and non-synchronization of flowering, which may avoid embryo abortion during embryo development and consequently as a key step for its successful invasion in China. These results open up new horizons for effective prevention and control of spread in the future.

Invasive plants generally present a significant enhancement in aboveground vegetative growth, which is mainly caused by variation in secondary cell wall (SCW) deposition and vascular tissue development. However, the coordination of the transcriptional regulators of SCW biosynthesis is complex, and a comprehensive regulation map has not yet been clarified at a transcriptional level to explain the invasive mechanism of S. canadensis. Here, RNA sequencing was performed in the phloem and xylem of two typical native (US01) and invasive (CN25) S. canadensis populations with different stem morphologies. A total of 296.14 million high-quality clean reads were generated; 438,605 transcripts and 156,968 unigenes were assembled; and 66,648 and 19,510 differential expression genes (DEGs) were identified in the phloem and xylem, respectively. Bioinformatics analysis indicated that the SCW transcriptional network was dramatically altered during the successful invasion of S.canadensis. Based on a comprehensive analysis of SCW deposition gene expression profiles, we revealed that the invasive population is dedicated to synthesizing cellulose and reducing lignification, leading to an SCW with high cellulose content and low lignin content. A hypothesis thus has been proposed to explain the enhanced stem growth of S. canadensis through the modification of the SCW composition.

Solidago canadensis L. is a regulated invasive alien species in China and was first recorded in the wild in Jiangsu Province. Despite widespread concern regarding its distribution and ecological associations, province-wide information on its current invasion status and associated plant community patterns in Jiangsu remains limited. To fill this gap, we conducted field surveys at 165 sites across Jiangsu Province and combined hierarchical clustering, plant-community diversity analysis, species-level analysis of accompanying-plant composition, redundancy analysis, and MaxEnt modeling to evaluate invasion-intensity patterns, associated environmental and anthropogenic factors, and plant-community responses in invaded communities. Solidago canadensis was recorded throughout the province, but invasion intensity was highest in southern Jiangsu. Hierarchical clustering classified the 165 sampling sites into three invasion-intensity groups. Group A (74 sites), concentrated in southern Jiangsu, was classified as the severe invasion group and showed generally lower plant diversity within the invaded-site dataset. Group B (60 sites) represented moderate invasion. Group C (31 sites), mainly distributed in northern and coastal Jiangsu, represented light invasion and retained relatively higher accompanying-plant diversity. Within S. canadensis-invaded communities, we documented 183 accompanying plant species from 43 families. Asteraceae and Poaceae were the most species-rich families, and annual or biennial herbs were the dominant life-form category. Species-level analysis further showed that accompanying-plant composition varied significantly along the invasion-intensity gradient (PERMANOVA, R² = 0.035), suggesting that differences in S. canadensis dominance were associated with detectable shifts in local plant assemblages. Redundancy analysis indicated latitude, transportation route density, and floating population density were closely associated with variation in S. canadensis invasion indicators and associated community variables, with soil pH, precipitation of the driest month, GDP, and motor vehicle ownership also contributing to the observed pattern. MaxEnt modeling identified southern and central Jiangsu as the main climatically suitable areas. This pattern was broadly consistent with the concentration of higher invasion intensity in southern Jiangsu. Nevertheless, field records in northern Jiangsu suggest that areas with lower predicted climatic suitability should also remain under continued monitoring. These findings suggest the need for coordinated management, particularly along major transportation corridors and in highly disturbed urban habitats. Control efforts should combine zoning management, source control, repeated removal, and habitat restoration tailored to local conditions.