- Name also: Northern Water Hemlock, Mackenzie’s Water Hemlock (USA)
- Family: Carrot Family – Apiaceae (Umbelliferae)
- Growing form: Perennial herb. Rootstock cylindrical–tuber-like, vertical, short, thick, with hollow compartments.
- Height: 30–150 cm (12–60 in.). Stem glabrous, glossy, hollow, joints with septa.
- Flower: Corolla regular (sometimes outermost flowers slightly zygomorphic), white–slightly reddish, approx. 5 mm (0.2 in.) broad; petals 5, entire–shallowly notched tips, tip curled inwards. Sepals 5. Stamens 5. Gynoecium syncarpous, with 2 styles. Inflorescence a compound umbel, secondary umbels (5–)10–20. Primary umbel without, secondary umbels with bracts.
- Leaves: Alternate, leaf base sheath-like, basal leaves long-stalked, stem leaves stalked–stalkless, stalk grooved. Blade ovate, 1–2 times pinnate. Leaflets lanceolate–narrowly elliptic (sometimes very narrow), with serrated margins.
- Fruit: Almost spherical, quite flat-sided, 2-sectioned, thick-ridged, reddish brownish yellow, approx. 2 mm (0.08 in.) broad schizocarp.
- Habitat: Shallow water in ponds, lakes, reservoirs, rivers, ditches, low-salt sea lakes, wet flood-influenced meadows. Fens and swamps in northern Finland.
- Flowering time: July–August.
Cowbane is probably the most dangerous of all Finland’s poisonous plants, and is far more poisonous than e.g. hemlock (Conium maculatum). Every part of cowbane contains cicutoxin, which is highly poisonous to virtually all mammals. Several wild mammals can eat cowbane without suffering ill effects but it is as dangerous to cattle as it is to people. A broken part of the plant can even pollute small bodies of water, and the run-off water can create a toxic area. The poison quickly causes symptoms like epilepsy which can at worst lead to death in a matter of hours. In the Finnish national epic Kalevala the bitter Lapp kills one of the main characters Lemminkäinen with a magical object made of cowbane. It is possible that the plant was used in days gone by to get rid of troublesome enemies.
Cowbane’s toxicity is all the more dangerous because it is very common, but luckily its favoured habitats in the shallow coastal water of nutritious waterways, does not attract much traffic due to the risk of sinking and the thick jungle of vegetation. It spreads via pieces of its rootstock, however, which wash up on land in the spring with possibly fatal consequences: cattle have grazed upon it and playing children have tasted it. Unlike other poisonous plants it doesn’t warn the eater with a bad smell or unpleasant taste: its stem and leaves have a dill-like fragrance and taste of parsley, while the rootstock, which is most poisonous of all, smells of celery and tastes sweet like parsnip.
Cowbane is divided into two variations, of which var. virosa, which grows in the south, is sturdier. Var. angustifolia is the more common in the swamps, fens and waterside meadows which are prone to flooding in the north of the country. Its leaflets are very narrow with slightly toothed margins and its inflorescence has sparser umbels.