Seed germination ecology of the aquatic winter annual Hottonia inflata

Freshly collected seeds of Hottonia inflata were buried in soil under flooded conditions in May 1991 and exposed to seasonal temperature cycles for 39 months. Seeds were exhumed at 1-, 2- or 4-month intervals and tested for germination on moist sand in light (14 h daily photoperiod) and in continuous darkness under 12/12 h thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20°C. On three dates, seed germination was tested under flooded conditions. In May 1991, 95% of the seeds were dormant, and they came out of dormancy during the summer of 1991, first gaining the ability to germinate to 90% or more in light at 30/15 and 35/20°C. By October 1991, seeds were non-dormant and germinated to 90-100% in light at 20/10 to 35/20°C. Seeds remained non-dormant during the rest of the study and did not exhibit cyclic changes in germination requirements. Only 1-13% of the seeds germinated in light at 15/6°C or in darkness at any thermoperiod. Seeds incubated under flooded conditions germinated to 0-2% at 15/6°C and to 58-95% at 20/10, 25/15 and 30/15°C. Although seeds have the potential to germinate in the field from April-October, the species functions as a winter annual. Apparently, its life cycle is regulated by favourable (e.g. low water level) and unfavourable (e.g. high water level) conditions for germination in its [B habitat in autumn and spring-summer, respectively.