Scientific: Guaiacum coulteri
Common: guayacan, pockwood, Sonora guaiacum, tree of life, wood of life
Family: Zygophyllaceae
Origin: A dry forest hardwood species endemic to the mountainous semi-tropical, deciduous forest Pacific coast regions of western Mexico from Sonora south to Oaxaca and also in Guatemala.

Pronounciation: Gu-A-i-a-cum COL-ter-i

Hardiness zones
Sunset
12 (in a warm microclimate) and 13
USDA 9-11

Landscape Use: Background screen, floral accent, multi-trunk small tree or large shrub in desert gardens.

Form & Character: Rangy when young becoming full and knarly with age, spreading, strangely symetrical, picturesque, informal.

Growth Habit: Upright and spreading to pendulous and weeping, sometimes to 20 feet often lower to only 5 feet with an equal to slightly greater than equal spread.

Foliage/texture: Leaves pinnately compound, medium to deep green, 6 to 10 oval leaflets per leaf, 1/2 inch long, nearly sessile, opposite or crowded on short spurs stems distinctly gray, stem nodes swollen; medium fine texture.

Flowers & fruits: Vibrant violet blue axillary flowers, five broad petals, extended yellow anthers, flowers occur either singley or in dense clusters, strongly attract bees; fruit inconspicuous, greenish reddish brown, winged, multicarpulate (2 to 4 lobes) capsule to 1/2 inch.

Seasonal color: Flowers mostly late spring, variable from intensely showy to sparse (particulary if overwatered). Here's a guayacan flowering intensely in late spring at a local Phoenix plant nursery (image courtesy of Sarah Celestian).

Temperature: Prefers warm temperatures and responds well to desert heat, freeze damage below 20oF.

Light: Full sun, becomes rank and sparsely foliated in shade.

Soil: Gravelly, well-drained soils are best.

Watering: Drought tolerant especially in winter, responds well though to summer water with vigorous growth (remember guayacan is a plant that's native to regions of high summer rainfall and dry winters).

Pruning: Prune conservatively to shape depending on landscape use, mostly to direct spread and control pendulous branching habit.

Propagation: Seed, cutting

Disease and pests: None

Additional comments: An interesting and beautiful large shrub for native Sonoran Desert plantings, not commonly grown by local nurseries.

Guaiacum coulteri has been extensively harvested in its southern native range. Over exploitation for timber in conjunction with habitat loss and a slow rate of regeneration has left G. coulteri threatened and has led to its listing on the IUCN Red List of Threatened Species and protection under CITES. There are approximately 25 species in the genus Guaiacum worldwide.