On the germination of Ruppia taxa in western Europe

Abstract

The germination of different Ruppia taxa, viz. Ruppia maritima L. var. maritima, Ruppia maritima var. longipes Hagström and Ruppia cirrhosa (Petagna) Grande, was studied in relation to chlorinity and temperature (under long-day conditions and in the dark, with and without a stratification period), desiccation and redox-potential. Seeds of R. maritima var. maritima germinated best in fresh water and at chlorinities up to 24%. The optimum germination temperature was 28°C. A stratification period of 2 months (4°C) resulted in an increase in germination at relatively low temperatures (16–20°C). The seeds proved to be very drought-resistant. Low redox-potentials (−300 mV) inhibited seed germination. Seedlings did not grow very well in fresh water. Mature plants grown from seeds that germinated at relatively low temperatures (16°C) produced flowers and fruits within a short period (± 8 weeks), whereas plants from seeds which germinated at relatively high temperatures (28°C) needed a very long time (at least 5 months) to produce flowers and fruits. The seeds of R. maritima var. longipes germinated best at relatively low temperatures (8°C). A few seeds of R. cirrhosa germinated occasionally under a variety of environmental conditions. The germination ecology of these taxa fits well within the circumstances that they are exposed to in their habitats in western Europe.