Are there keystone plant species driving diversity in midwest prairies?

There appears to be a small but important group of prairie plants capable of suppressing dominant plants, especially large warm-season grasses, through hemi-parasitism and chemical warfare, and thus releasing subordinate species. If this is truly the case, then introducing such keystone species into restorations and degraded remnants may help curtail domineering grasses and increase species diversity. Based upon my experience, leading candidates for this theoretical group include, from highest to lowest importance, wood-betony (Pedicularis canadensis), false toadflax (Comandra umbellata), northern bedstraw (Galium boreale), pussy-toes (Antennaria spp.), naked-stem sunflower (Helianthus occidentalis), showy sunflower (H. laetiflorus), downy paintbrush (Castilleja sessiliflora), Indian paintbrush (C coccinea), and tickseed (Coreopsis palmata). Testing the keystone role of these species may prove to be a fertile a-rea of research, and may result in a major step forward in understanding prairie plant community structure.