EARLY GAMETOPHYTE ONTOGENY OF GLEICHENIA BIFIDA (WILLD.) SPRENG.: PHYLOGENETIC AND ECOLOGICAL IMPLICATIONS

Past investigation of gametophyte ontogeny in Gleichenia bifida indicated that there was considerable plasticity in early developmental stages (spore germination to initiation of two-dimensional growth). Recent examination has shown that this early ontogeny is not so plastic and can be defined by a characteristic series of developmental stages. Cell divisions following germination result in a three-dimensional mass of cells which secondarily initiates the two-dimensional thallus. Early development as a three-dimensional mass correlates with other gametophyte and sporophyte features which indicate Gleichenia to be phylogenetically primitive. This pattern of early ontogeny may also be of adaptive significance in enabling the gametophytes to survive the environmental fluctuations of the exposed, bare-soil habitats which they colonize.