Linanthus parryae

Linanthus parryae is a species of flowering plant in the phlox family known by the common name sandblossoms. It is endemic to California, where it occurs in sandy, open habitat types in several regions from the Central Valley to the Sierra Nevada foothills and the Mojave Desert. This is a petite annual herb producing short stems just a few centimeters tall surrounded by hairy, needle-lobed leaves. The inflorescence, which often appears to sit directly on the ground tucked amidst the leaves, is a cluster of 
funnel-shaped flowers about a centimeter wide. The flowers are self-incompatible and are cross-pollinated exclusively by a Melyrid beetle, "Trichochorous" sp. Seeds germinate after winter rains in January to February, producing flowering plants in April and shedding seeds in May to June. Seeds are passively dispersed and remain viable for at least seven years, with no germination in dry years. The flowers on a plant may be white or blue. Flower color is mainly controlled by a single gene locus, with the allele for white flowers being recessive and the alleles of the blue flower being of the dominant type. Most populations have predominantly white flowers, with some populations mainly blue flowers, and some others with both blue and white flowered plants occurring at intermediate frequencies. The proportions of each color remain quite stable over time and in some locations there are sharp transitions from blue to white flowered populations. This uncommon phenomenon has made this species a model organism in studies of genetic variation.
For many decades a long line of geneticists and botanists, including Sewall Wright, Carl Epling, Harlan Lewis and T. G. Dobzhansky, have studied populations of this flower to determine the factors that influence this polymorphism. Color frequencies may vary for many reasons, including genetic drift and pure natural selection. Wright built his isolation by distance and Shifting Balance theories on genetic drift in this flower using data collected by Epling and Dobzhansky in the Mojave Desert. More recent studies place greater emphasis on the effects of natural selection on color frequency.