<p>The aim of this work is to study the effects of the brute aqueous extract (BAE) of seven species of the genus Miconia occurring in the Chapada do Araripe-CE on Lactuca sativa, in addition to identifying the classes of secondary metabolites present in the extracts. The treatments consisted of four concentrations of leaf extract (25, 50, 75 and 100%), in addition to a control (0%) of distilled water, with five replicates each in a totally randomized experiment design layout for seven days. The

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... following were assessed: number of germinated seeds, germination speed index (GSI), caulicle and radicle root length of the seedlings, occurrence of radical root necrosis, changes in the mitotic index and occurrence of chromosomal aberrations. The classes of secondary metabolites present in the extracts were identified through color changes and/or formation of precipitation. The brute aqueous extract of the leaves of M. albicans, M. alborufescens and M. stenostachya inhibited the germination of lettuce. All the BAEs of Miconia spp. had an adverse effect on the growth of the caulicle and radicle root of L. sativa. The extracts of M. albicans, M. ibaguensis, M. lingustroides and M. stenostachya were cytotoxic for the lettuce seedlings. Chromosomal aberrations were observed in all tested extracts. The metabolites found were hydrolysable and condensed tannins, flavonoids, flavones, flavanonols, chalcones, aurones and alkaloids. The tested species of Miconia showed inhibitory allelopathic activity within the parameters tested. The classes of secondary metabolites found could be responsible for the allelopathic and cytotoxic effects observed.</p>