Seed germination, seedling survivorship, and host preference of Agalinis auriculata (Michx.) Blake (Orobanchaceae), an Illinois, USA, threatened species

In a greenhouse study, we examined the parasitic relationship of Agalinis auriculata (Michx.) Blake (eared false-foxglove) (Orobanchaceae), an annual hemiparasitic plant, with potential host species. The two main objectives were (1) to determine host preference of the Illinois, USA, threatened plant, and (2) to determine percent seed germination and percent seedling survival in the presence of different potential host species. Overall, seed germination and seedling survivorship were very low. Agalinis auriculata had the highest seed germination and seedling survivorship, but produced no haustoria, when grown in pots with Sporobolus heterolepis (Gray) Gray. Haustorial development, as well as flower and fruit production, occurred when A. auriculata seedlings were paired with Helianthus occidentalis Riddell, Silphium terebinthinaceum Jacq., and Solidago rigida L. Flowers and fruits, however, were also produced by A. auriculata seedlings grown in pots with no host plant and in pots with a host plant but no haustorial development. This suggests that A. auriculata is a facultative hemiparasitic species. Our results also suggest that some plant species (i.e., Sporobolus heterolepis) may provide better germination conditions while others may serve as hosts for A. auriculata. Land managers should be aware of this information when considering reintroduction of A. auriculata into suitable sites.