region. The introduced water fern Azolla filiculoides is widespread throughout. Other plant species which are otherwise scarce or absent in the Bristol region but found in high concentrations on the North Somerset Levels are: flowering-rush (Myles, p. 210), lesser water-plantain (Myles, p.210-1), frogbit (Myles, p. 210-1), lesser pondweed (Myles, p.212-3), small pondweed (Myles, p. 212-3), hairlike pondweed (Myles, p213), opposite-leaved pondweed (Myles, p.213) and horned pondweed (Myles, p.213). The introduced Canadian and Nuttall's waterweeds are widespread throughout the levels (Myles p.211). References Bibliography Myles, Sarah (2000) The Flora of the Bristol Region External links Aerial photo at Windows Live Local North Somerset Plains of England Levels in the United Kingdom