Asclepias curassavica L. (Apocynaceae) a naturalized neophyte threatening the Hyrcanian biodiversity hotspot in North Iran

This study documents the naturalization of Asclepias curassavica (tropical milkweed) as a newly recorded alien species in the Flora of Iran. Native to the tropical Americas, A. curassavica has been widely introduced across Africa, Asia, Australia, and Europe – in recent decades, primarily as an ornamental plant. The first established population in Iran was observed in 2002 within the understory of a relict Populus caspica forest reserve in the Hyrcanian ecoregion of northern Iran. A second population was identified in 2015 near the initial site, occupying a slightly different habitat. Due to the persistence of these populations, its high reproductive potential and strong ability to spread, tropical milkweed can be classified as a naturalised alien. Its occurrence in a habitat of conservation importance is alarming, as it could have severe negative impacts on the native biodiversity of relict forests. Consequently, we advocate for the prompt eradication of this species and the formulation of a comprehensive management plan to prevent further spread. Additionally, this study provides a detailed morphological and ecological overview of A. curassavica, highlighting key distinctions from its closely related congeners within the genus Asclepias.