MORPHOLOGICAL, PHENOLOGICAL, AND BIOMASS TRAITS UNDERLYING THE INVASIVENESS OF FALLOPIA × BOHEMICA

Abstract

Fallopia × bohemica (Bohemian knotweed), an invasive hybrid of Fallopia japonica and Fallopia sachalinensis, is one of the most aggressive invasive plant species in riparian and disturbed habitats across Europe. In this study, we examined morphological, phenological, and biomass-related traits that may underlie the invasive potential of the species. The external morphology of aboveground shoots, leaf traits, epidermal characteristics, stomatal parameters, pollen morphology, and flowering phenology were examined within a single population during the 2018 growing season. Substantial intra-population variability was observed in plant height (125–337 cm), aboveground biomass (17.31–431.79 g d.w.), branching pattern, and total leaf area (1,000–12,000 cm²), largely driven by spatial position within the stand. Biomass accumulation was strongly associated with stem diameter and total leaf area, while shoot length showed a weaker relationship with branching intensity. Zone-specific variation in leaf morphology and petiole length enhanced light interception and contributed to dense canopy formation and pronounced shading. Leaves exhibited mesophytic epidermal traits, including hypostomatic structure and dense non-glandular trichome coverage, which reduce cuticular transpiration. Flowering occurred continuously but asynchronously within the population and provided an important nectar source for pollinators, despite limited sexual reproduction. Based on these observations, vegetative spread via rhizomes was inferred to be the primary driver of population persistence and expansion. Overall, the invasive success of Fallopia × bohemica appears to be driven by rapid biomass production, flexible shoot architecture, effective light capture, and strong competitive shading rather than by reproductive output. These findings highlight the importance of structural and biomass-related traits in shaping the species’ invasive performance.