Range expansion and phenotypic variation of tropical weed Amaranthus powellii in the temperate Kashmir Himalaya

This study presents the first report of range expansion of Amaranthus powellii S. Watson, a species native to tropical Central America, in the temperate Kashmir Himalaya, India. Field surveys and sampling were conducted at ten different sites spread across the study region. The species, being globally recognized for its aggressive weediness, has spread into agricultural fields, roadsides, wastelands, and riparian habitats in this Himalayan region. A taxonomic treatment, including detailed macro- and micromorphological descriptions, photographic documentation, and a comparison of diagnostic characters with the closely related species A. hybridus are provided to facilitate its field identification. The findings from multivariate analyses showed significant inter-population variation in key vegetative and reproductive traits, particularly leaf dimensions, inflorescence characteristics, and pigmentation intensity. Further, results from principal component analysis revealed substantial habitat-associated variation in morphological traits across populations. Populations in resource-rich agricultural habitats possess plants with taller height, broader leaves and longer inflorescences, while those in nutrient-poor wastelands showed relatively shorter height and intense anthocyanin pigmentation. Overall, the wide phenotypic variation observed across habitats indicates that A. powellii inhabits a diverse range of ecological conditions in the temperate Kashmir Himalaya. Given its high reproductive output and adaptability, A. powellii poses a potential risk to regional agriculture and biodiversity. Authentic identification using diagnostic traits, as provided by the present study, is essential for early detection and effective weed management. Looking ahead, future studies should focus on its reproductive biology and potential hybridization to better understand its invasive potential.