GROWTH AND SURVIVAL OF AZOLLA-FILICULOIDES IN BRITAIN - I - VEGETATIVE REPRODUCTION

Azolla filiculoides Lam, causes serious weed problems in Britain, but its long-term survival might be limited by winter death. The aim of th is study was to establish the low temperature responses and limitation s of A. filiculoides sporophytes. In the laboratory, normal vegetative growth was shown to continue at 5 degrees C. Reddening of plants was a response to low temperature and high light conditions which could be prevented by shading. Adult plants died after short (18 h) exposure t o -4 degrees C but survived sub-zero temperatures > -4 degrees C. Evid ence was found of seasonal changes in chill tolerance, but not in free ze tolerance. In outdoor culture, plants survived encasement in ice an d air temperatures to -5 degrees C. Additional evidence suggested that natural populations can readily survive air temperatures much lower t han this. Microclimatic effects are likely to be responsible for this discrepancy between laboratory and outdoor culture results. Three phen otyes were identified; survival, colonizing and mat forms.