Ferns--Florida

Old World Climbing Fern, Lygodium microphyllum is an aggressive nonindigenous plant that is on the verge of becoming a major ecological threat in South Florida. Currently, specific habitat characteristics that contribute to success or failure of its establishment are unknown. I studied the pattern of distribution of the fern in Florida's Big Cypress Swamp. Two similar forested wetland sites with high incidence of L. microphyllum infestation were assessed in order to identify broad-scale hydrological and physiographic conditions that may favor high susceptibility to L. microphyllum invasion. On each site, species richness, abundance and distribution of herbs, shrubs and trees were characterized. In addition, several parameters including elevation, substrate depth, percentage substrate water content, percentage substrate organic content, substrate texture, and photosynthetically active radiation were quantified. The patterns of distribution of L. microphyfum indicated that presence of the fern was dependent on relatively low elevation, relatively deep substrate and moderately high substrate water content.

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.