The germination requirements of Cladium jamaicense Crantz and Typha domingensis Pers. were studied under controlled conditions in the laboratory. Treatments included six temperature regimes, (constant temperatures of 15 20, 25, 30°C, and two fluctuating day : night temperature regimes of 25 : 10°C and 30 : 20°C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and water) and two O₂ levels (atmospheric and low (4.34%) O₂ concentration) using a complete randomized block design.

The average incubation period needed for seeds to germinate was shorter for T. domingensis (1.1–19.5 days) than for C. jamaicense (26–46 days) and the final germination percentage was higher for T. domingensis than for C. jamaicense (85 vs. 42 %). Cladium jamaicense only germinated with fluctuating temperatures whereas T. domingensis germinated at all temperature regimes. Light was required for T. domingensis seeds to germinate, whereas C. jamaicense could germinate at a reduced rate in the dark. Peat substrate had a positive effect on germination in both species. Peat substrate shortened the incubation period for seeds of both species, enhanced germination of T. domingensis, especially at low temperatures, and enhanced germination of C. jamaicense in the dark. Low oxygen availability did not influence the germination of C. jamaicense but enhanced germination of T. domingensis at low temperatures. Although the two species differ significantly in their germination requirements and responses to specific environmental conditions, germination of both these species was enhanced by environmental conditions typical of exposed water saturated mudflats or sediment surfaces. Typha domingensis produces a large number of small seeds, which do not germinate when covered by sediment. In contrast, C. jamaicense produces fewer and larger seeds, with resources able to support growth through a thin layer of sediment or detritus.