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The associated species to Senecio glaucus in the newly reclaimed desert near to Wadi El-Assiuty of the Eastern Desert at Assiut Governorate, Egypt were investigated over two years (2018 and 2019). The allelopathic potential of S. glaucus against two crop plants (Triticum aestivum and Eruca sativa) was also evaluated. Floristically, 65 species within 59 genera and 22 families were recorded (21 perennials and 44 annuals). Four families Asteraceae, Poaceae, Brassicaceae and Fabaceae captured about 54% of this flora. Therophytes are the predominant life form followed by phanerophytes. Chorological analysis revealed that cosmopolitan and Saharo-Arabian elements constitute the main bulk of the total flora of the studied area. Cluster analysis yielded four distinct groups. Stands of group A characterized by the absence of S. glaucus and highest species diversity. Stands of group B, C and D included the associated species of S. glaucus and characterized by the dominance of cosmopolitans, grasses and salt tolerant species. The ordination techniques revealed the significant difference between group A and the others and showed the strong correlation between its flora with organic matter. The other three groups were highly correlated with coarse soil texture and total salts. Thirteen species were absent from stands of groups B, C and D in which S. glaucus was dominant. Phytochemical analysis of S. glaucus showed the prevalence of total phenolics and flavonoids in its shoots, while terpenoids were the highest in its flowers. All fractions of the plant components completely prevented germination of E. sativa seeds but exerted different magnitude of inhibition on germination of T. aestivum caryopses (especially with MeOH, capitula and shoot extracts). Estimation of phytotoxicity revealed that aqueous, ethyl acetate and capitula extracts significantly inhibited the germination of wheat caryopses and reduced the elongation rates of hypocotyl and epicotyl, and hence the whole length of seedlings. [ABSTRACT FROM AUTHOR]