Ask Mr. Smarty Plants

There are 12 plants with the common name "evening primrose" in our Native Plant Database. There are 4 native to Arizona, so we chose to give you the ranges of those. 

Calylophus hartwegii ssp. pubescens (Hartweg's sundrops) -blooms yellow March to August. Range in Arizona from USDA Plant Profile. Range in North America. 

Calylophus serrulatus (yellow sundrops) - blooms yellow April to July.  Range in Arizona from USDA Plant Profile. Range in North America. 

Oenothera caespitosa (tufted evening-primrose) - blooms white April to August. Range in Arizona from USDA Plant Profile. Range in North America.

Oenothera speciosa (pinkladies) - blooms white or pink February to July. Range in Arizona from USDA Plant Profile.  Range in North America. 

To try to find out what were the traits of these plants that made them drought resistant, we found three websites that had a great deal of information:  Central Washington Native Plants  Plant Adaptations in Arid Environments; Plant Life in the World's Meditteranean Climates, by Peter R. Dallman, from University of California Press; Arizona Sonora Desert Museum Center for Sonoran Desert Studies How Plants Cope with the Desert Climate.

From this information, we found that the characteristics that the plants share that contribute to their survival are:

Long, narrow leaves, to avoid loss of moisture. Leaves also are hairy or downy, are blue-gray on the underside, and may fold up in the heat of the day.

Most of these plants bloom in the evening, and blooms close the next day when the heat begins to rise, again reducing moisture loss. 

Taproots-the seedlings quickly put down a taproot for moisture, and the mature plant develops a network of fine roots near the surface of the soil.

Plants may go dormant in summer, resprouting with rains.

From our Native Plant Image Gallery

Calylophus hartwegii ssp. pubescens

Calylophus serrulatus

Oenothera caespitosa

Oenothera speciosa