Format: ORAL

Eleonora Manzo1, Anna-Lena Kster1, Lina-Marie Deussig1, Franka Nei1, Alessio Papini2, Salvatore Tomasello1

1. Georg-August University Göttingen, Germany 2. Universitá degli studi di Firenze, Firenze, Italy

Xanthium orientale, an American species complex presently disseminated across the whole world, was first introduced in Europe via natural fiber trading, as the fruits stick easily to fibers owing to their peculiar spiny diaspores. Various lineages can presently be found in the continent, with X. orientale subsp. italicum being the first to have been observed in the wild around 1820. The presence of X. orientale in Europe has been hypothesized as a contributing factor to the contemporary decline of its indigeneous relative, X. strumarium. Herbaria play a crucial role in botany as they offer a wealth of untapped knowledge and a portal into plants historical past. The potential invasion paths of X. orientale subsp. italicum were traced using geographic profiling techniques and phylogenomic analyses of herbarium specimens. Moreover, the potential effect of allelopathy and competition for the decline of the native X. strumarium were studied through garden experiments. Geographic profiling is a technique initially developed in criminology, and then also applied for imputing biological invasion routes. The inferred spreading point for X. orientale subsp. italicum was the area close to Pavia or Monzambano. Phylogenetic analyses were conducted on nuclear and chloroplast data using network and ML tree approaches, suggesting a possible area of origin in Texas (US), around the town of Greenville. To test allelopathic effect of X. oriantale on X. strumarium, we compared germination and growth of seedlings under treatment (watered with X. orientale exudates) and control conditions. The presence of a significant effect has been observed on the growth of the two species. Concerning the competition experiments, we used dried biomass, number of burs and bur biomass as measure of fitness, showing a significant effect of the interspecific competition on X. strumarium.