Experimental sets of Mimulus cardinalis and M. lewisii plants were (1) exposed to pollinators and (2) shielded from pollinators at study sties in Red Butte Canyon and Big Cottonwood Canyon, Wasatch Mountains, Utah. The exposed plants produced 1,535 seedlings and the shielded plants only 1. Clearly, seed production is dependent upon cross-pollination. A few syrphid flies were observed visiting the flowers but no hummingbirds or bumble bees, although the latter two have been reported as the main pollinators of M. cardinalis and M. lewisii, respectively. No interspecific hybrids were produced even though the species are fully interfertile, indicating that pollinators are faithful to their species or that different parts of their bodies pick up and carry pollen to the two different species.
Vickery, Robert K. Jr.
"Pollination experiments in the Mimulus cardinalis–M. lewisii complex,"
Great Basin Naturalist: Vol. 50
, Article 6.
Available at: http://scholarsarchive.byu.edu/gbn/vol50/iss2/6