Nuphar Sm. (Nymphaeaceae) is a genus of aquatic macrophytic herbs distributed in the temperate Northern Hemisphere. Two species are known to occur in Kochi Prefecture in Southwest Japan, namely, Nuphar japonica DC. and TV. subintegerrima (Casp.) Makino. Both are rated as threatened species in the Prefectural Red Data Book, which ranked the former as Endangered (EN) and the latter as Critically Endangered (CR) (Kochi, 2000). Here, an assessment of their distribution, habitat and phenology in the Prefecture is presented. A total of 51 indiviudals at five localities were identified, and those are recognized as Nuphar japonica DC. and TV. subintegerrima s.l. (including the variety TV. japonica DC. var. saijoense Shimoda). In most populations, new leaf development occurred from February to April, with leaf senescence and dormancy occurring from August to March. However, late leaf development, as well as the complete absence of new leaf development, was observed at one locality. Upstream improvements for bank protection paved with concrete to river courses appear to pose the greatest threat to the persistence of populations in the Prefecture, with the risk of decline regarded as high at certain sites.
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