Mariosousa Species, Palo Blanco Tree, Willard's Acacia

Central Phoenix -- Palo Blanco deserves to be used more in landscaping. It is a beautiful small tree with lovely peeling white bark. Pa...Read Morelo 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.)

A spectacular Desert dweller which loves heat.

Deep in the heart of the Sonoran Desert, just south of the Mexican Border, ...Read Moreexists 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 cultivation where it has become more widely seen more recently.

Resembling a number of weepy Australian species from a distance, the canopy of Palo Blanco is a graceful mop of bright green gently swaying in a breeze. Interestingly, what look like long, shoestring-like leaves are modified stems which help the tree both conserve moisture, and help the tree gather energy from the sun. It is at the end of these that the tiny leaves, which resemble those of most Acacias, are seen.

Flowers which are produced on and off in late spring, or summer, resemble small cream colored bottle brushes and are reported to be slightly fragrant, though I really couldn't detect anything upon close inspection.

Seed, when produced, is never abundant, or as abundant as it can be in some of the weedier Acacia species. Pods are gold colored when ripe and quite papery. They can sometimes remain on the tree after ripening and opening.

The greatest attribute of this tree is the papery bark which closely resembles that of Melaleuca, or any of the thin-barked Birch species so commonly used in home landscapes from a distance. Shedding itself at fairly regular intervals, older bark is often painted in shades of tan, light brown, gold, or even splashes in pink-ish or orang-ish tones as it breaks away from the tree. Beneath this lie the smooth, bright white trunk the species is named for.

A tidy tree, shedding bark seldom becomes a litter issue below. Loving heat, reflected heat, staying relatively short, and growing slowly, Acacia willardiana can be used as a patio specimen, accented by lights to create an eye catching night time silhouette. It is also a great tree for under planting with cactus or succulent species which prefer a little shade. Many great specimens can be easily found while exploring Phoenix or surrounding areas.

Despite where it comes from, specimens which have shown up around Southern California seem to be doing well. A couple of nice (yet still small) specimens can be encountered in the Desert garden at The Huntington.

The only possible fault I can find with this tree is it's potential sensitivity to frost. Damage reportedly starts to occur somewhere in the high 20's. Overall hardiness seems to range between 24-28F, depending what info you reference.

Noting this, this species was another research candidate high on my must observe/document list when visiting the Phoenix area back in March. While I did see specimens with apparent post-freeze damage, I also encountered many others which where completely untouched. Can't say that about most of the Indian laurels (Ficus) I saw while driving around town.

Checking on the damaged specimens while back in the area recently, all looked well and recovered. I also encountered many more specimens which looked healthy as ever. In light of what I observed, It may be a great trial-worthy candidate for this portion of the S.F. Bay Area, or the warmer/drier spots in the East Bay/ Central Valley. Our only challenge might be excessive rainfall during the winter months.

I myself like the idea of a Paper bark Birch stand which is just as graceful, just as tidy, yet doesn't need much water to look great once established.

In a semi desert/Mediterranean type of climate, Birches are always fighting a loosing battle for water. Palo Blanco may turn out to be a great alternative.

A note about seeds:
When looking to germinate this species, Acquiring the freshest seeds possible seems to help with overall germination success. Tried several batches of older seed with 0% germination. After collection a small batch of fresher seed recently, I have at least 3 seedlings atm. Apparently this is a touchy Acacia species from seed and while young. Provide lots of heat, air movement and don't over water.

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 an...Read Mored 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.