3-Epi-Gibberellin A(63) (3-epi-GA(63)) was identified by full-scan GC-
mass spectrometry of a purified extract from culture media of prothall
ia of the fern, Anemia phyllitidis. This is the third antheridiogen, f
ollowing antheridic acid and 3 alpha-hydroxy-9,15-cycle-GA(9), in this
species. 3-Epi-GA(63) showed slightly less activity than antheridic a
cid in antheridial formation and dark spore germination assays.