Mimulus, the "Monkey Flowers", with about 100 or so species, is nearly worldwide in distribution, with a concentration of narrow endemics in California, particularly in the central Sierra Nevada, where I work, is worthy of more genetic study: in this post, I pose the question, "why flowers with nothing but large spots only ".
The basis for the question is based on my inspection of the large array of yellow mimulus photos posted on the web (Calphotos, Flickr). In most of the species, combinatorial of spots occur on the corolla: many have 3 large spots on each of the lower corolla lobes, along with an array of smaller spots near the throat. In some species, individuals are spotless (i.e. M. primuloides, M. tilingii, M. floribundus and M. guttatus, of which the three photos show spotless, small spots only, and large and small spots conditions). In other species, some individuals have only small spots, and lack the 3 large spots.
NEVER, in all of the photos I inspected, did I find an individual with only 3 large spots whilst the smaller spots were absent. The genetics of spot inheritance and assortment are worthy of study; are large spots linked in some complex fashion such that when any spot genes are expressed, 3 large spots are mandatory?