Is the common teasel (Dipsacus fullonum) carnivorous or was Francis darwin wrong?

Francis Darwin first suggested that the common teasel (Dipsacus fullonum L.), a biennial species, might be a carnivorous plant. He suggested that this species acquires nutrients from insects that drown in water-holding cups formed at the base of leaves that surround the stems. Since then, other biologists have made the same claim. To test this we addressed the question: does adding invertebrates as supplemental nutrients to water-filled cups of D. fullonum influence reproduction or are nutrients only obtained from the soil? We performed two factorial designed experiments (high-nutrient soil vs. low-nutrient soil) × (fed vs. control) to test this. Fed treatments involved either crickets or liquefied animal solution. We performed a third experiment where teasel plants were grown in nutrient deficient standard carnivorous plant soil mix to determine whether prey supplement influenced growth and reproduction. These experiments revealed that soil nutrients alone influence growth and reproduction. More seeds were produced by plants grown in high-nutrient soil; while curiously, a higher percentage of seeds germinated from plants grown in low-nutrient soil. When teasel rosettes were grown in carnivorous plant soil, plants did not grow, produce stems, or flower, even with animal solution. Thus we found no evidence suggesting common teasel is carnivorous.