Orobanche cumana

Galindo, J.C.G., de Luque, A.P., Jorrin, J., Macias, F.A. SAR studies of sesquiterpene lactones as Orobanche cumana seed germination stimulants. J Agric Food Chem 2002 50 1911-1917. 

Plants belonging to the family Asteraceae, including asters, daisies, and sunflowers, are rich sources of allelopathic sesquiterpenes and sesquiterpene lactones. Heliannuol A (19) and its related compounds heliannanes, found in sunflower leaves, are thought to be involved in the allelopathic effects displayed by the plants.8 Some sesquiterpene lactones such as dehydrocostuslactone (20), santamarine (21), and reynosin (22) have been shown to induce seed germination of root parasitic plants,9 especially of sunflower broomrape Orobanche cumana.10... 

Joel DM, Chaudhuri SK, Plakhine D, Ziadna H, Steffens JC (2011) Dehydrocostus lactone is exuded from sunflower roots and stimulates germinatirai of the root parasite Orobanche cumana. Phytochemistry 72 624-634. doi 10.1016/j-phytochem.2011.01.037... 

---