| Oxypolis canbyi, Sium suave, Thaspium, Osmorhiza longistylis, Ptilimnium|
Oxypolis rigidior, also known as cowbane, pig-potato, or stiff cowbane, is a poisonous species of flowering plant in the celery, carrot, or parsley family native to eastern North America. Cowbane is a perennial wildflower found in wet habitats.
Oxypolis rigidior Wikipedia
Oxypolis rigidior is 2-6 foot tall perennial herb of eastern North America. Its leaves are compound, odd-pinnate with 7-11 leaflets, and have variable shape. Umbels of 3 mm white flowers appear August to October. Flat fruits with conspicuous "wings" appear October through November.
The variable leaf shape may make identification challenging. Water hemlock, a related very poisonous species, which sometimes even shares the common name "cowbane", is similar, as is the closely related Savanna cowbane (Oxypolis ternata).
Two varieties have been described, O. rigidior var. rigidior and O. rigidior var. ambigua.
Both roots and top parts are poisonous to mammals.