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Mariosousa Species, Palo Blanco Tree, Willard's Acacia

Mariosousa willardiana

Family: Fabaceae (fab-AY-see-ee) (Info)
Genus: Mariosousa
Species: willardiana
Synonym:Acacia willardiana
View this plant in a garden



Water Requirements:

Drought-tolerant; suitable for xeriscaping

Average Water Needs; Water regularly; do not overwater

Sun Exposure:

Full Sun



Foliage Color:


Medium Green


10-12 ft. (3-3.6 m)

12-15 ft. (3.6-4.7 m)

15-20 ft. (4.7-6 m)


12-15 ft. (3.6-4.7 m)


USDA Zone 9b: to -3.8 C (25 F)

USDA Zone 10a: to -1.1 C (30 F)

USDA Zone 10b: to 1.7 C (35 F)

USDA Zone 11: above 4.5 C (40 F)

Where to Grow:

Grow outdoors year-round in hardiness zone


Plant has spines or sharp edges; use extreme caution when handling

Bloom Color:

Pale Yellow

Bloom Characteristics:

Flowers are fragrant

Bloom Size:

Unknown - Tell us

Bloom Time:

Mid Spring

Late Spring/Early Summer

Other details:

Unknown - Tell us

Soil pH requirements:

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

Patent Information:


Propagation Methods:

From seed; stratify if sowing indoors

Scarify seed before sowing

Seed Collecting:

Allow pods to dry on plant; break open to collect seeds

Properly cleaned, seed can be successfully stored


This plant has been said to grow in the following regions:

Maricopa, Arizona

Phoenix, Arizona(2 reports)

Tucson, Arizona

Gardeners' Notes:


On Mar 17, 2015, poeciliopsis from Phoenix, AZ wrote:

Central Phoenix -- Palo Blanco deserves to be used more in landscaping. It is a beautiful small tree with lovely peeling white bark. Palo blanco is not a good shade tree -- it is a lightly filtered shade, making it a good companion to other native desert plants. Ours was planted as a 24 inch box tree in 2008 and has grown very well. It gets a lot of water for a palo blanco -- being alongside a channel for the flood irrigation that occurs every other week from March to November. Despite one of the comments here, we have never seen any frost damage to our tree, even in the hard winter of 2012/13. (Recent Acacia taxonomic revisions have change the genus on palo blanco from Acacia to Mariosousa.)


On Sep 6, 2013, AridTropics from Chandler, AZ wrote:

A spectacular Desert dweller which loves heat.

Deep in the heart of the Sonoran Desert, just south of the Mexican Border, exists one of North America's most incredible trees. Gracing gravely hills or plains with a hint of shade, Acacia willardiana, or Palo Blanco, eeks out a living in some of the most desolate regions on our continent.

A species within the North American section of the Genus, this slow growing Acacia more closely resembles species growing in Australia than the scrubby, or thorny species one might encounter somewhere on the Great Plains or more commonly down in the Tropics. Unlike them, Palo Blanco employs some unique strategies to survive it's environment. Most of these adaptations are what makes this Acacia species so desirable in cultivatio... read more


On May 18, 2011, eileenderrick from Bahia Kino,
Mexico wrote:

I live off the coast of north central Sonora and there are many Palo Blanco Willardiana in our area. Last summer I collected seed pods and planted in a moist medium and soon had 4 plants. Very soon, approximately a month I had to transplant into ground so as to support rapidly growing plants. I now have, this spring, plants 4' to 5' tall. I did have them supported but after 3 months took supports off because I observed the strength in the Mother tree in the desert overlooking the Sea of Cortez.