<jats:title>Abstract</jats:title><jats:p><jats:boxed-text content-type="graphic" position="anchor"><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/mcontent.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:boxed-text><jats:p>A cinnamic acid ester, two dihydrocinnamic acid esters, a noroxyneolignan, a dibenzyl ether derivative, along with common aromatic compounds and flavonoids were isolated from the extracts of fresh leaves and twigs of <jats:italic>Oxalis pes‐caprae.</jats:italic> The structures of these aromatic compounds were elucidated on the basis of spectroscopic analyses, especially 2D‐NMR techniques. Their effects on the germination and growth of <jats:italic>Lactuca sativa</jats:italic> L. as standard target species have been studied at concentrations ranging from 10<jats:sup>−4</jats:sup> to 10<jats:sup>−7</jats:sup> <jats:sc>M</jats:sc>. The activities of some compounds were higher than that of pendimethalin, a commercial pre‐emergence herbicide.