The evolutionary divergence of five closely related populations of the yellow monkey flower. Mimulus guttatus was compared with the length of time the populations could have occupied the site and with the ability of the populations to intercross. Populations from the younger sites were found to be morphologically intermediate to populations from the older sites. Ability to intercross was not correlated with morphological divergence at this stage of evolution.
Hughes, Karen W. and Vickery, Robert K. Jr.
"Evolutionary divergence in closely related populations of Mimulus guttatus (Scrophulariaceae),"
Great Basin Naturalist: Vol. 35
, Article 5.
Available at: http://scholarsarchive.byu.edu/gbn/vol35/iss2/5