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The peripheral achenes can replace the mother plant in the following growing season, whereas the central achenes are well adapted for wind dispersal and thus for colonization of new sites. However, the extent of variation in germination characteristics was similar to that found in seed populations of homomorphic plants, which suggests that germination percentage and other growth characteristics do not contribute to widening the ecological amplitude. The habitat of most heteromorphic species, the morphs of which differ greatly in germination and/or growth characteristic, are deserts or highly disturbed areas where such differences are highly advantageous, but in the moderate habitat of L. saxatilis the differences may prove a disadvantage.

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The effects of stratification temperatures and burial in soil on dormancy levels of Carex pendula L. and C. remota L., two spring-germinating perennials occurring in moist forests, were investigated. Seeds buried for 34 months outdoors, and seeds stratified in the laboratory at temperatures between 3 and 18°C for periods between 2 and 28 weeks, were tested over a range of temperatures. Seeds of the two species responded similarly to stratification treatments, except for an absolute light requirement in C. pendula. Primary dormancy was alleviated at all stratification temperatures, but low temperatures were more effective than higher ones ͑ Ն 12°C͒. Dormancy induction in non-dormant seeds kept at 5°C occurred when seeds were subsequently exposed to 18°C. Dormancy was not induced by a transfer to lower temperatures. Buried seeds of both species exhibited seasonal dormancy cycles with high germination from autumn to spring and low germination during summer. Temperatures at which the processes of dormancy relief and of dormancy induction occurred, overlapped to a high degree. Whether, and when, dormancy changes occurred depended on test conditions. The lower temperature limit for germination ͑ Ͼ 10%͒ was 9°C in C. remota and 15°C in C. pendula. Germination ceased abruptly above 36°C. Germination requirements and dormancy patterns suggest regeneration from seed in late spring and summer at disturbed, open sites ͑forest gaps͒ and the capability to form long, persistent seed banks in both species.

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9°C in Mentha and 12°C in Lycopus and Stachys, and a maximum temperature of 33°C for Lycopus and 36°C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8°C in Mentha, 10°C in Stachys and 14°C in Lycopus (mean temperature 22°C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3°C and 18°C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures ( £ 12°C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12°C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12°C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8°C) were effective. At high test temperatures (25°C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.