Abstract
Aquatic flora was surveyed and their distribution maps were drawn in 12 irrigation channel networks along the Tama River, Tokyo. Of the recorded 15 aquatic plants, nine species were threatened or near threatened species listed on the red list of Ministry of the Environment or Tokyo Metropolis. Our result showed that irrigation channels had an important role for aquatic plants as their persistent habitat in the urbanized alluvial fan area. Comparing with past studies conducted from 1980s to 1990s, however, aquatic flora of this area degraded in some of the channel networks. Each species showed different distribution patterns. Distribution range of each species was concerned with their vegetative propagation character, such as root formation from plant fragments, rhizome formation, and the type of turion. Dispersal limitation between channel networks was also considered as a cause of limited distribution of some species. In addition, location of spring water seemed to determine restrictive occurrences of evergreen species which prefer cool water.
