What makes a successful invasive moss? Lessons from the reproductive biology and morphology of Campylopus introflexus (Hedw.) Brid.

Introduction The invasiveness of Campylopus introflexus is well documented, but its phenology remains unknown except for abundant spring-maturing sporophytes and caducous shoots.Methods Populations of Campylopus introflexus on a heathland in southern England were examined every 1–2 months over 4 years. Its reproductive biology and morphology were determined from field images, and light and scanning electron microscopy. To investigate the relationship between growth and sporophyte production, annual growth increments and sporophyte counts for wet and drier areas were paired and analysed statistically. For possible capillarity inside the perichaetia, female plants were placed in 1% methylene blue, and dye movements recorded.Key results Estimates of surface area occupied by males and females revealed a 75% preponderance of females. Following gametangia production in winter, it takes ∼16 months until sporophyte dehiscence in early summer. Young embryos remain quiescent through summer, and most sporophyte development occurs within the perichaetia, the sporophytes held there by basal spines on the calyptra. Exceptionally long archegonial necks within, closely embracing perichaetial leaves, act as capillary wicks, delivering sperm to stem tips. Sporophyte production relates strongly to annual growth in dry and wet substrates.Conclusions The invasiveness of Campylopus introflexus is probably explained by prolific sexual reproduction, tuned to seasonal weather cycles, rather than to rampant growth per se. Preponderance of females in our populations is attributed to greater allocation of resources to antheridium production rather than vegetative growth. Rampant sexual reproduction and invasiveness suggest C. introflexus as a model species to study climate change in bryophytes.