Seed ecology of two invasive aquatic plant species: Cabomba caroliniana and Sagittaria platyphylla

Abstract

Understanding seed ecology is important to contribute to the management of highly invasive aquatic plant species. Cabomba caroliniana A.Gray (cabomba) and Sagittaria platyphylla (Engelm.) J.G. Sm. (sagittaria) are both significant water weeds in Australia. While cabomba is a fully submerged aquatic plant producing few seeds, sagittaria is an emergent species and a prolific seeder. The results from laboratory experiments showed that sagittaria germinated well at constant temperatures ranging from 17 to 29°C, with the highest rate of 98% germination at 21°C. Germination only occurred under light which indicates that buried seeds could not germinate even from shallow depth of 0.5 cm. In the laboratory, a controlled aging test predicted that sagittaria seeds could retain viability for 3 to 5 years. Seeds were also treated with two herbicides florpyrauxifen-benzyl and flumioxazin at five different concentrations for 24 hours to examine the effect on seed mortality. Results showed that the germination was unaffected (100%) by both herbicides. Cabomba is thought to only produce viable seeds in two populations in the Northern Territory and Victoria while other populations are thought to be sterile. There is little information available on its seed ecology. Recently, seeds of cabomba have been detected in multiple populations in Southeast Queensland and Northern New South Wales. When tested with tetrazolium (0.5%) the seeds were confirmed as viable. However, seed production was estimated to be very low at ca. 8 seeds m-2 in the warm months (December to June), and ca. 3 seeds m-2 from June to December. Cabomba seeds were successfully germinated in the laboratory, but more seed materials are now needed before a full understanding of this species seed ecology can be determined.