Allelochemicals are natural chemicals released by plants and/or microbes that inhibit the growth of other plants/microbes. An extract from 'Chrysanthemum morifolium' tissue bleached 'Lemna ' and inhibited the germination of lettuce and mustard seed. Extract purification using liquid/liquid partitioning and subsequent 9:1 and 1:1 DCM:acetone fractions eluted from a silica column retained the inhibitory properties in both fractions. Further purification using reversed-phase (C18) column chromatography yielded three fractions, of which a 100% methanol fraction maintained the inhibitory properties. Regions of an HPLC chromatogram collected from the 100% methanol fraction did not inhibit 'Lemna' growth. Possible explanations include synergistic effects between compounds that were lost in the final stage of the purification, or a compound with a concentration too low to be effective. Literature comparison supports the conclusion that the putative allelochemical(s) are either acidic or neutral, and during successful inhibitory bioassays the compound(s) concentration was in the microgram range.