Reproductive biology and gametophyte morphology of the Hawaiian fern genus Sadleria (Blechnaceae) relative to habitat diversity and propensity for colonization*

Comparative ontogenetic studies were made of the gametophyte generation grown from spores taken from natural populations of the four species of Sadleria. Significant differences were found between species in the nature of the perispore, presence or absence of a terminal trichome on the one-dimensional filament, and the sequence of gametangia formation. Breeding tests were also conducted and sporophytes screened for recessive lethals. Three species were found to have intergametophytic mating systems and heterozygosity for sporophytic lethals. Of these, S. cyatheoides and S. souleyetiana have retained the capability for monogametophytic reproduction, whereas S. pallida has not. The fourth species, S. squarrosa, has a prolonged gametophyte generation intolerant of higher light intensities. Correlations between frequency in nature, habitat diversity, ability to colonize newly formed lava flows, reproductive biology and syndromes of the gametophyte generation are made.