Oenanthe crocata, hemlock water-dropwort (sometimes known as dead man's fingers) is a flowering plant in the carrot family, native to Europe, North Africa and western Asia.

The upper part of the roots include five or more obovoid, pale yellow, fleshy tubers up to 6 cm long, which exude a yellowish oily fluid when cut that stains the skin.

[1][2] The lower leaves are 3–4 times pinnate, triangular, with oval toothed leaflets 10–20 mm long, that are basally tapered to the stalk (cuneate).

[3][4] Like other species in the genus, hemlock water-dropwort has compound umbels, with 12–40 smooth rays (stalks), 3–8 cm long, which carry the smaller umbellules.

The specific epithet "crocata" comes from the same root as crocus, and refers to the saffron-yellow colour of the oil that exudes from ducts in the tubers,[11] although this is difficult to observe in fresh specimens.

[12] The native distribution of hemlock water-dropwort is concentrated along the Atlantic seaboard of Europe, from the coast of the Netherlands south to Portugal and Spain, rapidly becoming rare inland.

[17] In France, where it is known as "oenanthe jaune safran", it is considered unthreatened ("Least Concern", or LC), although in some départements it is rarer; for example, in Île-de-France and Picardy it is classified as Critically Endangered (CR).

[19] Hemlock water-dropwort is a plant of shallow fresh water streams, marshes, lakes, ponds, canals and wet woodland.

It is most abundant in such a habitat, sometimes forming dense stands alongside ditches or around pools and extending over hundreds of square metres.

[24][23] Its Ellenberg values in Britain are L = 7, F = 8, R = 6, N = 7, and S = 1, which show that it favours damp, reasonably sunny places with neutral soils and moderate fertility, and that it can occur in slightly brackish situations.

[25] The flowers are unspecialised, meaning they can be pollinated by many species of insect, which are attracted to the nectar that is secreted onto the exposed surface of the stylopodium.

[27] The toxic principle in the plant is oenanthotoxin, a polyunsaturated higher alcohol that is a potent convulsant and works by blocking the γ-aminobutyric acid (GABA) system in the brain.

[31] The Scottish botanist John Lightfoot, in his 'Flora Scotica' (1777) related the experience of the illustrator Georg Ehret, who found that "the smell, or effluvia only, rendered him so giddy that he was several times obliged to quit the room" until he opened the door and windows so that he could finish his work.

[29] Scientists at the University of Eastern Piedmont in Italy wrote that they had identified Oenanthe crocata as the plant responsible for producing the sardonic grin.

[35][36] The essential oils from the seeds of O. crocata have been shown to have moderate antibacterial effect against Enterococcus faecalis and Bacillus lentus.

[38] In the past, extracts from this plant have been used in medicine, for example as a treatment for epilepsy,[39] and in Ireland it was apparently commonly used in a poultice for treating skin disorders and even cancers.