Chinese lobelia; Lobelia chinensis
A small perennial herb native to East Asia, often found in moist places. The Japanese name literally means 'ditch-hider'.
Chinese lobelia was blooming along the footpath between the rice paddies.
Written 溝隠し, literally “ditch-concealer,” from 溝 and 隠す. The name refers to the plant’s low, spreading growth, which can cover the edges of wet ditches.