water pimpernel
noun
1A brooklime or water speedwell (genus Veronica) (now rare ).
2(Often with distinguishing word) any plant of the genus Samolus (family Primulaceae), typically having rosettes of leaves and racemes of small white or pink flowers; also called brookweed.
Origin
Late 16th century; earliest use found in John Banister (1532/3–?1610), surgeon.