Abstract:Allelopathy of Ageratina adenophora plays an important role in its invasion. However, we have little knowledge of its allelpathic effects on ferns. In Petri dish bioassays, the inhibitory potential of aqueous leachates from roots, stems and leaves of Ageratina adenophora was studied on the spore germination and gametophyte development of Macrothelypteris torresiana. All leachates inhibited the spore germination and growth of first rhizoid of M. torresiana and inhibitory effects increased with increasing leachate concentrations. Root leachates proved most inhibitory. Gametophyte rhizoids of M. torresiana treated with stem and leaf leachates of A. adenophora exhibited erect, similar with those of the control. However, gametophyte rhizoids of M. torresiana treated with root leachates of A. adenophora were erect, curving, or swollen. Moreover, curving and swollen rhizoids increased with increasing concentrations. As time went by, rhizoids treated with root leachates were not so curving and the swollen almost disappeared. Possible causes were discussed in this study. The increasing concentrations of leaf leachates also delayed the stages of gametophyte development. With the treatment of root leachates, the delay was more obvious. Thus A. adenophora inhibited the spore germination and gametophyte development of M. torresiana and the root leachates were most inhibitory.