Responses of seed germination of Xanthium orientale L. and Xanthium spinosum L. to temperature

Species of the genus Xanthium (cocklebur) are invasive plants widespread all over the world. In Bosnia and Herzegovina, Xanthium orientale L. was an invasive species, while Xanthium spinosum L. was an economically harmful weed species. The reason these species are spread over vast areas and across various climate conditions must be attributed to their biology, particularly the biology of their seeds. Germination of populations of X. orientale and X spinosum at a temperature range of 15 degrees C to 40 degrees C over 2 to 20 days ranged between 15.0% ( X. spinosum ) and 90.0% ( X. orientale ). By means of the application of a statistical model, a positive correlative dependence of temperature and time on seed germination was determined ( X. orientale = 80.70%, X spinosum = 62.20%), which provided a possibility of modelling the seed germination of Xanthium species in various ecological conditions. The optimal germination temperature for both cocklebur species was 30 - 35 degrees C. As the germination of seeds was recorded at all researched temperatures (15, 20, 25, 30, 35 and 40 degrees C), it points to a wide ecological valence for the considered abiotic factor. These results suggest that the unique germination biological characteristics of the Xanthium genus made it extremely easy for the species to form monodominant communities in new habitats and climate-changing environments quickly.