Water dispersal of the invasive complex Fallopia: The role of achene morphology

•Achene morphology is responsible for the variation of buoyancy.•Buoyancy differs between stands colonizing the different rivers.•Watercourses seem to be a preferential pathway to Fallopia dispersal.•Achene morphology may influence the water dispersal and the spread of the taxon.

Watercourses are powerful vectors of species colonizing riverbanks. The morphological traits of propagules that increase buoyancy can enhance the spread of those species throughout the landscape. The goal of this study was to analyse the water dispersal capabilities of achenes of the morphologically diverse hybrid complex Fallopia x bohemica through the relationship between achene morphology and buoyancy.The achenes of F. x bohemica were collected from 60 stands growing along watercourses in the Rhône-Alpes region (France). Achene buoyancy was measured experimentally using a load cell. The shape of the achenes was quantified by principal component analyses based on elliptic Fourier descriptors of 2D wing shape. A spatial distribution analysis of the stands along different watercourses was performed to determine the relationship between the achene buoyancy and the dispersal potential.Across the 60 studied stands, flotation was positively correlated to the achene wing area. The flotation force, corrected for the achene mass, differed between the F. x bohemica stands sampled and was correlated to achene shape; in particular, the rounded achenes had a higher buoyancy than the elongated ones. Furthermore, the spatial autocorrelation of the flotation force suggested dispersal along rivers.These results highlight the water dispersal potential of the achenes of the Fallopia complex. Even if vegetative dispersal affects dispersal patterns, the morphological variation of achenes leading to different dispersal capabilities should be considered a major evolutionary driver of the complex.