| Summary: | <i>Prosopis juliflora</i> (Sw.) DC. Is highly recognized for its invasive character and its detrimental effects on different plant species across the world. In this study, a field survey was performed to assess the impact of <i>P. juliflora</i> on the surrounding native plants, followed by the effect of different concentrations of its aqueous leaf extract on seed germination and seedling growth of selected Qatari flora. Our field observations indicated a high prevalence of new recruitments of <i>P. juliflora</i> than other native-associated plants in the study site. Germination percentage and/or seed radicle length of the test species: <i>Acacia tortilis</i> (Forssk.) Hayne, <i>Prosopis cineraria</i> (L.) Druce, <i>Sueda aegyptica</i> (Hasselq.) Aellen, <i>Halopeplis perfoliata</i> (Forssk.) Bunge ex Schweinf. & Asch, and <i>P. juliflora</i> were significantly (<i>p</i> ≤ 0.05) reduced by the extracts at different concentration levels. Moreover, the germination rate of <i>A. tortilis</i> was not affected; however, the seed germination of <i>P. cineraria</i> was significantly affected at concentrations of 6 and 8 mg mL<sup>−1</sup>. The seed radicle lengths at 2 mg mL<sup>−1</sup> were significantly reduced for both plant species. The seed germination and radicle length of <i>S. aegyptica</i> and <i>H. perfoliata</i> were significantly decreased at 2 mg mL<sup>−1</sup> of extract of <i>P. juliflora.</i> Furthermore, the height and biomass of the seedlings of <i>Aeluropus lagopoides</i> (L.) Trin. ex Thwaites, <i> Caroxylon imbricatum</i> (Forssk.)<i>,</i> and <i>Tetraena qatarensis</i> (Hadidi) Beier & Thulin were significantly reduced by the aqueous extracts at 6 and 8 mg mL<sup>−1</sup>. The aqueous extract reduced the seed germination and seedling growth at 6 and 8 mg mL<sup>−1</sup>, indicating an autotoxic effect. Such allelopathic behavior of <i>P. juliflora</i> designates the potential investigation of using its allelochemicals as naturally based herbicides in agrosystems.
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