An erect or decumbent herbaceous perennial. Stems hairless, from 20 to 60cm tall, with four narrow wings running down their length. Leaves amplexicaul, elliptic to oblong, 10 to 40mm long, with undulate margins, and with some black marginal glands. Flowers 1.5 to 2cm across, in a lax panicle. Petals 5, bright yellow, tinged red on the back, and sometimes with a few black glands. Sepals unequal, with black glands.
Local:Rare in Gibraltar. Found as a weed in well-watered cultivated plots.
Global:Found in far western and south-western Europe and northern Africa.
Flowers from July to August
Grows on damp and wet soil, and freshwater margins.