Arizona-Sonora Desert Museum Digital Library

Description

This is a summer annual that grows nearly prostrate to 3 feet (0.9 m) across with sparse divided foliage. Flowers are over an inch across (about 3 cm) with 5 petals. In early morning they open a bright orange with darker striations, then fade to pale orange with the afternoon heat. In the southern part of the range, pink-flowered plants appear as well.

Range

Summer poppy grows from northern Arizona to Texas and south to Colima, Mexico; it is also found in southern Baja California. It occurs in desert and tropical habitats but is most abundant in desert grassland, where it creates mass displays of color reminiscent of the desert blooms of spring annuals.

In the desert it occurs as widely scattered individuals or occasional small patches.

Notes

Summer poppy seeds have a long dormancy. They will usually not germinate until they are several years old, and presumably remain viable in the soil for many decades.

Kallstroemia parviflora and K. californica look vegetatively similar but have much smaller orange flowers. Seedling summer poppies may also be confused with the related puncture vine or goat-head (Tribulus terrestris). Puncture vine has tiny yellow flowers and bur-like seeds with strong, sharp spines.

The seeds of puncture vine, a European weed, are well adapted to dispersal by rubber tires, and the plant now grows along the runways of every temperate airport in the world (not to mention most bicycle paths). Once a serious pest in North America, its numbers have been effectively reduced by introducing a weevil that feeds specifically on puncture vine seeds. There is disturbing evidence, however, that the beetle is now attacking summer poppy. Biological pest control (integrated pest management) is much less damaging to the environment than the use of broad-spectrum pesticides, but it too can go awry and must be employed very carefully.

The caltrop family is a small one of about 250 species. The best-known (and most-hated) species is goat-head or puncture vine (Tribulus terrestris), a weed introduced from Europe. Lignum vitae (Guaiacum spp.) is perhaps the hardest wood in the world. Though there are only a few caltrop species in our region, one of them is among the most abundant and widespread desert plants and another is a showy summer wildflower.