Distinguishing Silphium in Illinois by their leaves
S. terebinthinaceum: Large upright arrow-shaped leaves at base of plant
https://www.inaturalist.org/observations/31934856
S. intergrifolium: leaves opposite going up stem but not joined together
https://www.inaturalist.org/observations/31935369
S. perfoliatum: leaves opposite going up stem and joined together forming a cup
https://www.inaturalist.org/observations/29797854
S. lacinatum: leaves highly lobed and pointed
https://www.inaturalist.org/observations/29409542
