Coulter's Wrinklefruit (Tetraclea coulteri) blooms here in the Sonoran Desert anytime from April to September, but this native, perennial wildflower mainly blooms here in the late summer after several weeks of summer monsoon rains. Coulter's Wrinklefruit has tubular, 5-lobed, creamy white flowers and distinctive, 4-lobed, wrinkled, green fruits that give this plant its common name.
Coulter's Wrinklefruit plants have pairs of variably toothed leaves and axillary flower clusters along the erect stems. Despite its non-verbena-like appearance, Coulter's Wrinklefruit is in the Verbena Family (Verbenaceae).
Like many other Sonoran Desert plants with white, tubular flowers, Coulter's Wrinklefruit is nocturnal-flowering. The flowers open fully in the evening and close sometime the next morning. The photograph below shows the normal daytime appearance of Coulter's Wrinklefruit flowers.
I had a very difficult time getting a photograph of fully open Coulter's Wrinklefruit flowers. Unfortunately, both places where I had previously found them growing were not safe to visit after dark. One site with flowering Coulter's Wrinklefruit was along an extremely rough and remote dirt "road" and the other was next to a roadway overpass near some scattered liquor bottles and tatty sleeping bags. I was finally able to photograph fully open Coulter's Wrinklefruit flowers on a nighttime wildflower hunt for Huachuca Mountain Rocktrumpets (Macrosiphonia brachysiphon). Although I didn't find any Huachuca Mountain Rocktrumpets with flowers that evening, I did find a patch of blooming Coulter's Wrinklefruit, so the nighttime wildflower hunt was still a success.