Sand verbena, Abronia fragrans, has a moth pollination syndrome, or a suite of floral characters modified by natural selection driven by moth pollination.

Its flowers are open all night but closed all day, and long corolla tubes prevent bees from taking nectar but is ideal for moths with long tongues. Moths follow plumes of floral fragrance from sand verbena until they are within sight of the bright, conspicuous white globes of 25 to 80 flowers where they sip a nectar reward.

Although sand verbena has a large geographic range, it is limited to sandy habitats in Texas, New Mexico, Arizona, Utah, Colorado, Oklahoma, Kansas, Wyoming, Montana, Nebraska, South Dakota and North Dakota.

While sand verbena is described as having white flowers that open only at night, populations in northern Texas and southwestern Oklahoma have a range of flower colors from light pink through fuschia, and they also differ from the majority of populations for the times that flowers open and close.

The plants with pink or fuschia flowers remain open until late morning, and they reopen in early evening, allowing considerable visitation by bees and butterflies. Measurements of pollination success in the pink and fuschia populations showed that diurnal or daytime pollination contributed 18% of the pollination success, in contrast to nothing at all in the remainder of the geographic range of the species.

These data are consistent hypothesis that diurnal pollinators were a selective force producing and maintaining novel flower color and diurnal presentation of open flowers in the mornings and late afternoons. The long corolla tubes frustrate bee efforts to collect pollen or nectar but holds nectar available to virtually all butterflies.

Butterflies are visiting diurnally — most common among them is the skipper Lerodea eufala, the Eufala skipper. These data and other observations suggest the hypothesis that the Eufala skipper applied selective pressure to change flower color from white to pink or fuschia and to modify the times that flowers open and close.

How could a butterfly apply selection pressure? This terminology unintentionally suggests that the butterflies had a plan and the organization to apply it. But that was not the case. If some flowers did not close exactly at sunrise and if a small butterfly pollinated them, enhancing their seed set, the genes that influenced tardy closing of flowers would become more common in the next generation.

The butterfly did nothing more than sip nectar from a large globe of flowers, nor did the sand verbena do anything to achieve an intended goal. The metric of natural selection is the relative number of offspring produced by competing genotypes of sand verbena. Genes that had been rare produce more seeds, making those genes more common.

Sand verbena is in the genus Abronia, which has about 20 species, all in North and Central America. All thrive in sandy environments, and it is known that 14 of the 20 species have psammophory, a defense to herbivory that is more commonly called sand armor. The armor is assembled when wind-blown sandy grit adheres to sticky exudates on stems and leaves.

I first encountered psammophory when photographing dwarf lupine in the Maze in Canyonlands, and since then, I thought it was a rare defense. But a scientific article whose title begins with “Chewing sandpaper” lists over 200 psammophorous species in 88 genera in 34 families. Sand armor is not a rare defense; it is geographically widespread and has evolved many times. Experimental studies show that sand armor reduces herbivory — remove it from stems and leaves and the plant suffers more herbivory than when the armor was intact. Add more sand, and the plant suffers less herbivory.

While sand verbena has a large geographic range, some species of Abronia have tiny geographic distributions. One example is Yellowstone sand verbena, A. ammophila, which is adapted to and endemic (found nowhere else) to the lake shores in Yellowstone National Park.

An obligate relationship was found recently when a new species of moth, Copablepharon fuscum, was discovered in 1995 on the shores of the Salish Sea (Georgia Straight and Puget Sound). The sand-verbena moth was found on just a few beaches and spits on Vancouver Island and Whidbey Island, and it only occupies sites with wind-blown sand and large and dense populations of A. latifolia, yellow sand verbena, which is found along Pacific Shores from Baja to British Columbia.

The sand-verbena moth uses yellow sand verbena as its host plant, meaning that it is the site of oviposition and the sole food consumed by the caterpillars. The caterpillars have specialized mouth parts allowing them to manipulate around grains of sand.

I know I will never see a sand verbena nor a dwarf lupine without the phrase “chewing sandpaper” popping into my thoughts.

Jeff Mitton is an emeritus professor of the University of Colorado Boulder Department of Ecology and Evolutionary Biology.