Ecological study on alien Amaranthus spinosus L. in the Egyptian Nile Valley.

Amaranthus spinosus L. is a member of the Amaranthaceae family, commonly known as the spiny amaranth, or spiny pigweed. It is native to the tropical Americas, but is present on most continents as an introduced species, noxious weed, and can be a serious weed of rice cultivation in Asia. In Egypt, the Nile Delta, particularly Cairo, is the home of spiny amaranth; however, it has recently been recorded in the Nile Valley (Aswan area) colonizing different habitats such as roadsides, depressions, Khor and river banks. This study aimed to study the current distribution of spiny amaranth in the Aswan area and its associated species. It also aims at studying their life and growth forms, habitats, soil characteristics, local and global distributions, local threats, and spiny amaranth seed characteristics. Five sites along the river Nile in Aswan city was surveyed from the period of 2018 until 2025 in four identified habitats (Roadsides, depressions, khor, and river banks). Forty species were recorded associated with spiny amaranth, belonging to 38 genera and 16 families. Therophytes (15 species) followed by phanerophytes (14 species) were the most represented life form. All recorded species inhabit the Nile region, and most of the 12 taxa were pantropical. Most studied species (32.5% of the total threatened species) suffer from at least one type of threat. They mostly suffer from habitat loss due to industrial, urban, and tourist development. Soil samples were analyzed for edaphic variables. The relative importance of a certain environmental factor on the distribution of the recorded species across the four habitats were performed using PCORD (v6.22 software). The spiny amaranth seed colors are mainly dark brown to reddish brown, lenticular shape, glabrous and matte surface, acute apex, and obtuse to rounded base, hilum marginal, sub-basal, and slightly eccentric. Its length ranged from 7.24 to 7.84 mm, and its width varied between 7.27 and 7.77 mm. The authors recommended that monitoring the behavior of alien species and conducting ongoing surveys are crucial for biodiversity conservation.