The reproductive biology of Agalinis auriculata (Michx.) Raf. (Orobanchaceae), a threatened North American prairie inhabitant

We examined the reproductive biology of the hemiparasitic threatened prairie species, Agalinis auriculata (Michx.) Raf., eared-false foxglove (Orobanchaceae), in two populations located at the Midewin National Tallgrass Prairie in Illinois. Populations flowered from late August through mid-September, and individual plants bloomed for an average of 8 d; typically two flowers per plant opened each day. Buds opened in the early morning hours between 0530 and 0630 hours, with the anthers dehiscing at this time. Stigmas reached peak receptivity ca. 2 h later, followed by corolla abscission shortly afterward. Breeding system experiments indicated that flowers readily self-pollinate without reduction in fruit set, seed set, or seed mass compared with outcrossed individuals. The primary floral visitors were Bombus impatiens (Apidae) and Melissodes bimaculata (Anthophoridae). On the basis of phenological and breeding system data, A. auriculata is a self-compatible species that self-pollinates in the absence of floral visitors; however, when pollinators are present, outcrossing can occur. The autogamous nature, in combination with a healthy reproductive output, indicates that the decline of this species might result from other aspects of its biology, such as seed germination and availability of host plants.