Abstract
One thousand and eight (Chikugo Plain) and 674 (Saga Pl.) creeks of the area were investigated in the autumn of 1974. In each creek, about 0.1 ha of water surface was examined as a unit area to identify emerged, floating-leaved and free-floating aquatic weed species growing there. Submerged ones were excluded because they were rarely problematic in utilizing water of creeks.
Thirty four species were found in investigated creeks, and the 4 of them, that is, waterhyacinth [Eichhornia crassipes (Mart.) Solms], knotgrass (Paspalum distichum L.), hairly subspecies of knotgrass (Paspalum sp.) and parrotfeather (Myriophyllum brasiliense Camb.), were the most troublesome weeds in the area. Unimportant, but widely distributed 11 species were Ashikaki (Leersia japonica Makino), cutgrass (Leersia Sayanuka Ohwi), wild rice (Zizania latifolia Turcz.), common reed (Phragmites communis Trin.), frogbit [Hydrocharis dubia (Bl.) Backer], lotus (Nelumbo nucifera Gaertn.), waterchestnut (Trapa natans L. var. bispinosa Makino), Onibishi (Trapa natans L. var. quadrispinosa Makino), giant duckweed [Spirodela polyrhiza (L.) Schleid, ], duckweed (Lemna paucicostata Hegelm.) and azolla (Azolla imbricata Nakai). Other 19 ones were infrequently found in those creeks.
As a mean number, there grew about 1.9 aquatic species in each creek. Sixteen% creeks were free of weeds, and 69% were infested with 1 to 3 species. More than 4 species were found only in 15% creeks.
