Plants have the ability to interfere with other organisms in their immediate environment, a phenomenon called allelopathy. Allelopathy is a common phenomenon in nature (Qian Chemosphere 75(368):375, 2009). The use of allelopathic compounds for the development of new agrochemicals has several benefits as opposed to common synthetic products. Cognizant of reports on the allelopathic action of medicinal and invasive plants, 118 Iranian plants from 104 species which belongs to 34 families have been screened for allelopathic volatiles by the dish pack method. Materials and methods A total of 118 plants (104 species) belonging to 34 families were collected in 2009 from the tropical, subtropical and temperate regions of Iran. The Dish pack method as described by Fujii et al. (Weed Sci Technol 45(80):81, 2000) utilized for screening the presence of allelopathic volatiles released from different parts of the plant specimen. This method can be used to recognize allelopathic properties very easy and quickly. Results Results of bioassay with lettuce seed (Lactuca sativa cv. Great Lakes 366) revealed that 23 species elicited growth inhibitory actionwith the greatest (C96% reduction) observed in the inflorescences of Achillea wilhelmsii and Achillea filipendula. Furthermore, a high suppression (83–95 %) in radicle elongation was observed in lettuce exposed to: flowers of Achillea nobilis, Lavandula vera, and Perovskia abrotanoides; fruit of Ruta graveolens; seeds of Bunium persicum and Trachyspermum copticum; leaves of Achillea biebersteinii, Pulicaria gnaphalodes, Ziziphora clinopodioides, Zataria multiflora; gum of Ferula foetida; and stigma of Crocus sativus. On the other hand, 14 species instead exhibited growth-promoting properties. Of these, the greatest promoting effect were exhibited by the leaves of Cardaria draba, Verbascum speciosumand Urtica dioica eliciting 69 %, 56 %, and 53 %, respectively, which had longer radicles compare to the control.

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