Euphorbia palustris, the marsh spurge or marsh euphorbia, is a species of flowering plant in the family Euphorbiaceae, native to marshland throughout much of mainland Europe and western Asia.

It is an herbaceous perennial growing to 90 cm (35 in) tall and wide, with narrow leaves turning red and yellow in autumn, and persistent, bright acid yellow flower-heads (cyathia), 15 cm (6 in) across, in spring.

[2][4] It prefers permanently moist conditions in full sun, hence the common name "marsh spurge" and the Latin specific epithet palustris, "of marshland".

Euphorbia palustris has gained the Royal Horticultural Society's Award of Garden Merit.

[7][8] Like all euphorbias, all parts of the plant are toxic if ingested, and cut stems produce an irritant sticky sap.