How to identify Hemlock Water dropwort

The hemlock water-dropwort, also known as dead man's fingers,is a flowering plant in the carrot family, Apiaceae, native to the British Isles, Western Europe and the Iberian Peninsula. 

Each branch looks like a mini version of the whole shoot, with a stem and leaf stems branching off in opposite pairs,  which are 2-4 times pinnate (splitting off in pairs of leaves or stems) the leaves are much more rounded than that of cow parsley or poison hemlock, but still has a toothed edge.

The flowers grow in an umbel (this is part of the umbellifer group). There 12-20 thin stems growing from the top of the stem which at the top are 15+ more thin stems each with a single flower with 5 boomerang shaped leaves around a creamy off white centre and long white anthers with a black tip. 

The small umbellules, which are 5–10 cm in diameter, have 6 or more bracteoles at their base and numerous flowers on short pedicels. The flowers are white, almost actinomorphic with five subequal petals, the outer ones being slightly larger. There are also five conspicuous sepals which are triangular, sharply pointed, and persistent.

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. This plant is a possible candidate for the "sardonic herb", which was a neurotoxic plant referred to in ancient histories. It was purportedly used for the ritual killing of elderly people and criminals in Nuragic Sardinia.

The hemlock water-dropwort shares a genus with many other superficially similar European water-dropworts, all of which are poisonous but not deadly.