The effect of medicinal plant extracts on growth of Lemna aequinoctialis

Medicinal plants contain an array of natural chemicals and often research has focussed on their pharmacological value. During 2004/2005, we investigated the potential of bioactive chemicals in medicinal plants to inhibit plant growth using a Lemna (Lemna aequinoctialis) bioassay. Aqueous extracts from plant parts (viz. leaf, stem, bark, root etc.) of 8 test species (Ageratum conyzoides, Acacia farnesiana, Acacia melanoxylon, Alphitonia excelsa, Castanospermum australe, Chamaesyce hyssopifolia, Melaleuca quinquenervia and Phyllanthus virgatus) were added to Lemna nutrient medium resulting in a 2% extract concentration. Then using digital photographs, the growth of the Lemna was measured for 7 days using Scion computer software. Extracts from all eight species affected the growth of L. aequinoctialis, with the strongest growth inhibition coming from stem and bark extract of A. melanoxylon (98% and 91% growth inhibition, respectively), leaf extract of P. virgatus (91% growth inhibition) and leaf extract of A. conyzoides (88% growth inhibition).