赤桉 (Eucalyptus camaldulensis) 為桃金孃科 (Myrtaceae) 桉樹屬 (Eucalyptus)植物，原產於澳洲，剋他效果十分明顯。研究者以赤桉葉萃取物進行生物檢定(bioassay) 之結果，顯示利用桉葉粉末及水萃液處理禾本科、豆科植物和莧科雜草的種子，皆能抑制發芽和影響胚根與胚軸伸長，而利用桉葉精油處理種子，更可達到100%的發芽抑制率。分析其精油主要成分為1,8-cineole 及α-pinene 等單萜類化合物，其中α-pinene 對植株的傷害是引起氧化逆境產生活化氧族破壞膜系的完整性，造成離子滲漏現象；而1,8-cineole 對於植物造成的毒害則為抑制植物細胞有絲分裂的進行。

River red gum (Eucalyptus camaldulensis), native to Australia, has been reportedthat the secondary metabolites released from this plant have significant allelopathiceffect. Based on the responses of several bioassay materials to allelochemicals releasedfrom river red gum, leaf powder and water extract inhibited seed germination and bothradicle and hypocotyl elongation of weeds including Gramineae, Leguminosea andAmaranth spp.. In addition, essential oil of river red gum showed a complete inhibitionof seed germination. The primary ingredients of this essential oil are two monoterpenes,i.e., 1,8-cineole and α-pinene, the former prevents cell mitosis and the latter promotesgeneration of reactive oxygen species and subsequent damage of cell membrane.