Extracts of Clitoria ternatea L.: Phytochemical Profile and Allelopathic Activity in Lactuca sativa L.

Developing plant-based weed-management tools from allelopathy requires evidence that phytotoxicity is both chemically supported and biologically reproducible. This study examined whether the allelopathic activity of Clitoria ternatea L. varies among leaves, stems, and a leaf + stem mixture, and whether such variation is associated with organ-specific chemical traits. Hydroethanolic extracts were characterized by histochemical, phytochemical, and thin-layer chromatographic analyses and tested in vitro on Lactuca sativa L. at 75, 150, and 300 mg L−1. All matrices contained phenols/tannins, flavonoids, and triterpenes/sterols; however, the leaf extract showed the strongest coumarin signal, the presence of saponins, and the richest TLC pattern. These chemical differences were matched by a clear biological gradient, with inhibitory activity ranked as leaf > leaf + stem > stem. At 300 mg L−1, the leaf extract reduced germination to 71%, radicle length to 10.23 mm, and vigor index to 1372, while increasing mean germination time to 5.78 days and yielding the most negative allelopathic response index (−0.663). Overall, the results identify leaves as the main reservoir of phytotoxic metabolites in C. ternatea and support their prospective use in botanical weed-management research.