Heracleum mantegazzianum

Name and classification

Heracleum mantegazzianum Sommier & Levier
Family Apiaceae

Common names

giant hogweed

Disseminule

fruit segment (mericarp)

Description

Fruit a schizocarp with 2 mericarps, each with 1 seed. Schizocarps split along commissures (ventral faces) of mericarps. Mericarps elliptic to obovate, compressed dorsiventrally, (7)9–12(14) mm long, (5)6–8(11) mm wide, 0.1–0.5 mm thick (schizocarp 1–2.25 mm thick), dorsal side with 5 longitudinal filiform ribs extending from base to stylar end: 1 central, 2 intermediate, and 2 lateral and winged; 4 reddish-brown vittae (oil glands) between the ribs, ca. three-quarters as long as fruit, obclavate; ventral side lacks central and intermediate ribs, but has 2 vittae half length of the fruit. Surface dull to somewhat glossy, glabrous to sparsely villous, dark straw yellow colored. Stylar end of schizocarp pointed, wrinkled and darker brown. Undehisced schizocarp may have persistent pedicel remnant. Embryo rudimentary; endosperm readily visible, oily.

Identification considerations

The mericarp of Heracleum mantegazzianum can be distinguished from other similar fruits in the genus by its conspicuously expanded vittae.

Similar species

Heracleum sphondylium L. ssp. montanum (Schleich. ex Gaudin) Briq. (=H. lanatum Michaux.) (non-FNW)

Distribution

Europe: Austria, Czechoslovakia, Denmark, Finland, France, Germany, Georgia, Hungary, Ireland, Italy, Netherlands, Norway, Sweden, Switzerland, United Kingdom; Asia: Iran, Russia (central); Australia; North America: Canada, United States

native to Caucasus region between Black and Caspian Seas

Habitat

wet areas, along streams and rivers; naturalized on waste ground, near houses, in vacant lots, along railways, roads

General information

Heracleum mantegazzianum is indeed a “giant” biennial or perennial herb, up to 5 m tall, with huge compound leaves and umbels up to a diameter of 0.75 m. It can form dense canopies, outcompeting native riparian plants. The plant’s leaves and particularly stem exude a clear, watery sap that photosensitizes skin, causing a condition known as photodermatitis. Blisters and burns may result on subsequent exposure to the sun. The dried fruit is used as a spice in the Middle East.

fruits

fruits

commissures (ventral faces) of mericarps (with parts broken off)

commissures (ventral faces) of mericarps (with parts broken off)

A, ventral face of mericarp; B, dorsal face of mericarp; C, longitudinal section of mericarp showing embryo; D, transverse section of schizocarp; drawing by Lynda E. Chandler

A, ventral face of mericarp; B, dorsal face of mericarp; C, longitudinal section of mericarp showing embryo; D, transverse section of schizocarp; drawing by Lynda E. Chandler