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(Oenanthe crocata)

Hemlock Water-Dropwort is an umbellifer (in other words, a member of the Carrot Family); it is an attractive plant, but a potentially deadly one: "The tubers are sweetish-tasting, but very poisonous, due to a series of polyacetylenes. The active principle is oenanthetoxin, a convulsant poison, which can cause rapid death with few symptoms. Fatal cases of human poisoning have occurred when the leaves were mistaken for those of celery, or the tubers for parsnips" [T.G.Tutin in "Umbellifers of the British Isles", BSBI Handbook No.2, 1980].

[Around 2014, the plant was mentioned several times in articles and letters in local newspapers, though these ever more frequently began to call the plant "Hemlock". This is wrong, and a very unhelpful confusion. Hemlock (Conium maculatum) is an entirely different plant from Hemlock Water-Dropwort, although both species are poisonous and are members of the Carrot Family.]

Hemlock Water-Dropwort is a plant of ditches, pondsides, and other wet places; it is most common in the south and west of Britain. It is described as a "calcifuge", meaning that it will not be found growing in chalky, alkaline soils. This species occurs in abundance here alongside the cycle route; this area, close to the river, provides a suitably damp habitat, and the soil here (and throughout much of the surrounding region) is generally fairly acidic.

For some other common but very poisonous plants, see NS4984 : Foxglove and NS8279 : Monk's-hood (an Aconitum species).

(An aside: the genus name Oenanthe is also found in zoology: specifically, among birds. This is possible because plants and animals are governed by different codes of nomenclature. Compare the comments at NS3977 : A fungus on conifer wood.)