reproductive biology of Lygodium microphyllum and L. japonicum, two invasive fern species in Florida

Lygodium microphyllum and L. japonicum are two non-indigenous invasive climbing ferns which are currently spreading through Florida. The reproductive biology of both species was examined to determine if their reproductive strategy partially explains this spread. Gametophytes of both species were grown in vitro as isolates and pairs to examine reproductive strategies. L. microphyllum appeared to be capable of both outcrossing and selfing, while in L. japonicum intragametophytic selfing appeared to be the primary mode of sexual reproduction. Outcrossing in L. microphyllum appeared to be the result of an antheridiogen system that affected sexual expression of neighboring gametophytes and subsequent sporophyte production. Seventy-eight percent of L. microphyllum isolates produced sporophytes while over ninety percent of the L. japonicum isolates produced sporophytes. The high selfing rates achieved by both species likely facilitated their spread through Florida, while the outcrossing ability of L. microphyllum may increase its adaptability and invasive potential.