Abstract Antheridiogens in two species of Schizaeaceous ferns, Lygodium circinnatum and Lygodium flexuosum, were analyzed by gas chromatography-mass spectrometry. In L. circinnatum, gibberellin A73 (GA73) methyl ester (GA73-Me), which had originally been identified in L. japonicum, was identified as a principal antheridiogen, and the methyl esters of five known GAs (GA9, GA20, GA70, GA88, and 3-epi-GA88) were also identified as minor antheridiogens. In addition, four compounds corresponding to isomers of monohydroxy-GA73-Me were detected. One of these was shown to be 12β-hydroxy-GA73-Me, the parent acid of which has been allocated the GA assignment GA96. The other three compounds, tentatively named X1, X2, and X3, have not been fully characterized. In L. flexuosum, GA73-Me was also identified as a major antheridiogen, with X2 being detected as a minor one. The total antheridium-formation activity in the culture medium of 7-week-old prothallia of L. circinnatum and L. flexuosum was more than 1000 times higher than that of L. japonicum. On the other hand, the response of gametophytes of the former two Lygodium ferns to GA73-Me was more than 100 times lower than that of L. japonicum.