Role of temperature, light and date: seeds were exhumed from soil on germination of four wetland perennials

Seeds of the four wetland perennials Cyperus odoratus L., Gratiola viscidula Pennell, Penthorum sedoides L. and Scirpus lineatus Michx. were buried in soil and exposed to yearly seasonal temperature cycles. At monthly intervals for 30.5 or 31 months, seeds were exhumed and tested at daily alternating (12/12 h) temperature regimes of 15/6, 20/10, 25/15, 30/15 and 35/20°C in light (14 h photoperiod) and darkness. Seeds of all species had an absolute light requirement for germination. Freshly matured seeds of C. odoratus and P. sedoides were conditionally dormant, while those of G. viscidula and S. lineatus were dormant. Seeds of all species became non-dormant during winter; however, those of C. odoratus and G. viscidula never gained the ability to germinate at 15/6°C. Buried seeds of C. odoratus and P. sedoides remained non-dormant during the remainder of the study, while those of G. viscidula and S. lineatus exhibited an annual conditional dormancy/non-dormancy cycle.