This species is parasitic mostly on plants of a wet habitat. The following is a list of the hosts of my specimens; 3 on Aster, 4 on Boehmeria, 2 on Campsis, 3 on Cephalanthus, 1 on Dianthera, 1 on Decodon, 1 on Eupatorium, 1 on Helianthus, 1 on Hypericum, 19 on Impatiens, 1 on Lactuca, 1 on Laportea, 2 on Mentha, 1 on Phytolacca, 1 on Polygonum, 1 on Rubus, 2 on Saururus, 2 on Salix, 3 on Solidago, and 1 on Vernonia. This species is variable in the size and proportion of its flower parts. Two specimens of var. vulvivaga from Steuben County were cited by Yuncker (Univ. of Illinois Biol. Monographs 6: 66. 1921) but in 1932 he refers this variety to the species. Accordingly, a report from Porter County by Lyon is referred to C. Gronovii by Buhl (Amer. Midland Nat. 16: 252. 1935).