An investigation into the cytology and breeding behaviour of the large asiatic Reynoutria species (R. japonica and R.sachalinensis), which were introduced into the British Isles in the last century and are now a significant component of the British Flora. A number of colonies have been examined morphologically and cytologically; hybrids have been identified and artificially re-synthesised in the laboratory. The sex-expression of the Reynoutria taxa has been examined, and has been found to be gynodioecious. R. japonica var. japonica has been found only as male-sterile plants in the British Isles, which has made it particularly susceptible to hybridisation with Fallopia baldschuanica (the commonly grown garden plant Russian Vine). Seed production and viability, and the role of seed production in the colonization of Britain has also been investigated.\ud Chromosome counts and karyotypes have been produced of Reynoutria taxa and of the closely related Fallopia species. 2c DNA amounts have been determined, and Giemsa and fluorescent banding techniques employed.\ud A comprehensive synonomy has been produced, and the relationship between the genera Fallopia and Reynoutria discussed. One conclusion of this research is that the genus Reynoutria should be incorporated into the older genus Fallopia
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