SafePlants

Mariosousa willardiana (Palo Blanco)

Mariosousa willardiana, formerly known as Acacia willardiana, is a graceful tree appreciated for its delicate appearance and adaptability to arid environments. It is also commonly known as Palo Blanco tree, palo liso, guinola, Willard Acacia, Willard's Acacia, and White-barked Acacia.

The Spanish common name, Palo Blanco, translates to "white stick," referring to its distinctive white bark.

Considerations for Pets

• While explicitly stated as thornless in some instances, the plant is related to the Acacia genus, which often includes thorny species. Check carefully before planting.

Taxonomy and Nomenclature

• Scientific Name: Mariosousa willardiana (formerly Acacia willardiana)
• Family: Fabaceae (Pea Family, Leguminosae)
• Kingdom: Plantae
• Taxonomic Rank: Species
• Synonyms: Acacia willardiana Rose
• The accepted name is Acacia willardiana Rose, within the genus Acacia.
• A proposal to conserve the name Acacia willardiana against Prosopis heterophylla has been made.
• The plant's classification has undergone revision, with it now being classified in the genus Mariosousa.
• Family is now Mariosousa willardiana (Rose) Seigler & Ebinger.

Distribution and Habitat

• Native to Arizona and Mexico, specifically the Sonoran Desert and rocky slopes and canyons of southern regions.
• Found in foothills thornscrub environments.
• A sub-tropical native of Sonora, Mexico.

Morphological Characteristics

• A small tree, typically reaching 15-20 feet in height and 10-15 feet in width.
• Leaves feature a mid-rib with 5-6 leaflets at the end, also described as a flattened petiole.
• Blooms in spring with creamy, light yellow, rod or bottle-brush-like flowers (catkins).
• The bark peels, revealing a smooth, white inner bark.
• Form is slender and graceful, with arching branches and sparse foliage.
• Foliage is deciduous in some environments.

Growing Conditions

• Hardy to approximately 23-25 degrees Fahrenheit.
• Prefers full sun to partial sun exposure.
• Requires little water once established.
• Suited for Sunset Zones 8, 9, 12-24.

Ecological Role

• Native to the Sonoran Desert and well-adapted to arid environments.

Quirky Facts

• The tree's foliage can be so sparse that it is difficult to see even when in full leaf.

Interactions with Other Organisms

• Mention of interest for narrow spaces that need some interest.

Further Information

• Germplasm Resources Information Network (GRIN), U.S. Department of Agriculture Agricultural Research Service.
• ARKive (for photos and facts).
• Encyclopedia of Life.
• Arizona State University Herbarium.
• B and T World Seeds' database.
• PubMed for jnal article concerning free amino acids in the seeds of Acacia willardiana.
• Discover Life.