- Perennial forb with tuberous-thickened rootstock.
- Ascending to erect, to 2 m, glabrous, glaucous, hollow with cross-paritions, sometimes purplish at nodes, simple to branching.
Stem and node.
- Alternate and sometimes basal, glabrous. Lower leaves long-petiolate, the blades to 40 cm long, broadly ovate or triangular-ovate, 2-3x pinnately compound. Upper leaves with shorter petioles, 1-2x pinnately compound or occasionally simple. Leaflets to 12 cm long, lanceolate, tapered at the base, occasionally with basal lobes, the margins sharply toothed, the lateral veins ending at the sinuses between teeth.
- Compound umbels, terminal and axillary, mostly long stalked. Involucre absent or less commonly of 1-4 bracts, these shorter than the rays, spreading to ascending at flowering, linear, with sharply pointed tips. Rays usually numerous, 1.5-6.5 cm long, often unequal in length. Involucel absent or more commonly of 3-7 bractlets, these mostly shorter than the flower stalks, linear to broadly lanceolate, with thin, white, papery margins, tapered to sharply pointed tips.
- Numerous in each umbellet, on stalks 2-10 mm long. Sepals minute triangular teeth. Petals 5, white, obovate, margins deflexed, to 1.3 mm broad, 1.1 mm long, apiculate and inflexed at apex. Stamens 5, alternating with petals, erect to spreading. Filaments white, 1.2 mm long, glabrous. Anthers whitish, 0.2 mm long. Ovary inferior, 2-locular, glabrous. Styles 2, 0.1 mm long.
- Schizocarps 2.0-4.5 mm long, broadly oblong-elliptic in outline, flattened laterally, glabrous, dark brown to reddish brown with pale ribs, glabrous, the mericarps with 5 ribs, these blunt and somewhat corky.
- May - September.
- Sloughs, streambanks, pond margins, wet prairies, other wet areas.
- Native to U.S.
- Numerous other members of the Apiaceae (hemlock/carrot family).
- This may be the most toxic vascular plant found in North America. It is fairly common throughout Missouri, and also ranges throughout the U.S. and Canada. The inflorescences appear similar to many other plants in the family. A key feature of this species is the lateral veins of the leaflets, which end at the notches between the teeth rather than at the tips of the teeth. This is clearly visible in the leaflets photo above, and it's a good character for identification. Note that the bracts subtending both the main umbel and the umbellets can be either present or absent.
The plant is said to have a pleasant licorice or anise scent when crushed, but contact should be avoided due to the possibility of skin absorption of toxins. All parts of the plant are poisonous, but the roots, swollen lower stems, and new growth are considered the most toxic. The potency of the plant is such that children have been reportedly been fatally poisoned by using pea shooters or whistles fashioned from pieces of the stems or roots. Even individuals who recover from poisoning can suffer long term effects, such as retrograde amnesia and impaired cognition. The main toxins are acetylenic alcohols, with cicutoxin being one example. Interestingly, these are chemically very different from the alkaloids found in the closely related poison hemlock plant (
Infraspecific divisions have been revised since Steyermark's time. Currently, two varieties are recognized in Missouri:
(S. Watson) G.A. Mulligan. These differ in subtle aspects of the ridges on the fruit surfaces. The latter taxon is relatively rare.
Photographs taken off Hwy H, Shannon County, MO., 6-23-04 (DETenaglia); also at Shaw Nature Reserve, Franklin County, MO, 6-30-2008, Otter Slough Conservation Area, Stoddard County, MO, 7-18-2009, and Busch Wildlife Area, St. Charles County, MO, 7-18-2013 (SRTurner).