Scientific: Caesalpinia gilliesii
Common: There are many common names for this plant. They are in no particular order:  bird of paradise shrub, bird of paradise bush, desert bird of paradise, or yellow bird of paradise (even though the flowers have bright red stamens). This is problematic and demonstrates why use of scientific names to identify plant material is important.
Family: Fabaceae
Origin: Native to Argentina and Uruguay, but has now naturalized in portions of the Chihuahuan and Sonoran Deserts in close proximity to inhabited areas.

Hardiness zones
Sunset 12-16, 18-23
USDA 9 - 11

Landscape Use: Seasonal accent, quick background though canopy is too sparse to make a screen, nice tropical shrub for transition areas in oasis landscape design themes

Form & Character: Partially evergreen shrub, irregularly rounded and spreading, sparse, open, festive, warm, vulnerable

Growth Habit: Moderate growth to 8-10' tall with equal spread. Very brittle wood.

Foliage/texture: Leaves twice pinnately compound, leaflets to 1/4" and less, light green, graying with age, stems without spines but with well defined lenticels, fine texture

Flowers & fruits: yellow flowers with red filaments on terminal spikes, fruit are green pods in terminal clusters turning to brown pods in summer that are heavy and weigh down branches. 

Seasonal color: Festive yellow/red flower color in spring and fall

Temperature: Heat loving like C. pulcherrima. Partially to fully deciduous during coldest winters.

Light: Full sun

Soil: Tolerant. Regular fertilization will increase foliar canopy density which is otherwise typically sparse to open.

Watering: Needs summer water

Pruning: Head back lightly after bloom only as needed to promote a more excellent shape. Unlike C.  pulcherrima, don't severely prune as it is slower to recover.  

Propagation: Seed

Disease and pests: White flies

Additional comments: Good medium, open canopied accent plant. This medium-sized, slower growing accent shrub evokes semiarid subtropical connotations and attracts hummingbirds. The tanins found in the seeds are mildly toxic causing severe gastrointestinal distress that usually subsides after 24 hours.