Heracleum

1. Primary umbels with ca. 70–120 rays; undersides of leaves with the main veins with sparse, short, straight spicules or nearly glabrous; reddish oil canals on the fruit up to 0.5–0.9 mm wide, extending ca. 75% of the way from apex to base of the fruit.

H. mantegazzianum

1. Primary umbels with ca. 10–50 rays; undersides of leaves with the main veins pubescent with straight to curly hairs; reddish oil canals on the fruit mostly less than 0.5 mm wide, extending ca. 50–60 (–70)% of the way from apex to base of the fruit.

2. Basal leaves merely ternate; leaf rachises with slender, often reflexed or curly hairs mostly not more than 1 mm long.

H. maximum

2. Basal leaves clearly pinnate; leaf rachises with thick, spreading hairs up to ca. 2 mm long.

H. sphondylium

All species found in Heracleum

Heracleum mantegazzianumGIANT HOGWEED 
Heracleum maximumCOW-PARSNIP 
Heracleum sphondyliumHOGWEED, EUROPEAN COW-PARSNIP 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 27, 2017. http://michiganflora.net/genus.aspx?id=Heracleum.