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.
A threatened species: 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.
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, fountain like, spreading, strangely symetrical, picturesque, informal.
Growth Habit: Evergreen, woody, broadleaf (leaflets are small) perennial broadleaf shrub to small tree, upright and spreading to pendulous and weeping, sometimes to 20-feet tall, typically shorter in Phoenix to sometimes only 5- to 10-feet tall, but always 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; fruits inconspicuous, yellowish green to 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.
Public service announcement: 'Hort clods' pay attention!! Guayacan is a gorgeous plant that should NEVER be sheared!
Propagation: Seed, cutting
Disease and Pests: None
Additional comments: Guayacan is an interesting and beautiful large informal shrub to small tree (with training) for native Sonoran Desert plantings, not commonly grown by local nurseries.
Taxonomic tidbit: There are approximately 25 species in the genus Guaiacum worldwide.
