Multi-scale analysis of two annual Helianthus species naturalization in Argentina

The localization of two wild annual Helianthus species recently established in Argentina, H. annuus and H. petiolaris, were found to be connected with climate, soil, and agroecosystem variables. The habitats of both species, being mainly roadsides, were strongly related to disturbance, but they were also found in riparian areas and within crops. Microhabitat conditions allowed clear differentiation among the species’ preferences, H. petiolaris appeared associated with sandy soils with low organic matter content, while H. annuus showed preference for more fertile and fine textured soils. In the western region of the country, irrigation strongly modified the environment favoring H. annuus. No variables allowed characterization of the three sites, where both species grew together.