Sonoran palo blanco
Mariosousa heterophylla
Family: Fabaceae
OTHER NAMES
Willard Acacia
CHARACTERISTICS
Small semi-evergreen, thornless tree, 20’h, 15’w. White to cream colored, rod shape flowers appear in spring and mature into dark brown, 3" to 8 " long seed pods over the summer. This tree has an airy canopy.
LANDSCAPE USE
This is a great accent tree with a magnificent, shiny white trunk. Perfect for commercial spaces, or yards with little room.
GROWING CONDITIONS
AN EXPLANAITION OF TERMS USED
SUN full sun
WATER moderate to low water
SOIL not picky, but well-drained
HARDINESS hardy to 20-25°F, plant in a warm microclimate
BASIN high to middle zone
CONTAINER can tolerate containers for some time
NUTRITION low
MAINTENANCE very little
ECOLOGY
Larval host for Gray Hairstreak (Strymon melinus), Marine Blue (Leptotes marina), Ceraunus Blue (Hemiargus ceraunus ssp. gyas), various owlet moths (family Noctuidae), and geometer moths (family Geometridae). Flowers attract butterflies and lots of other nectar feeders.
Photo by Mountain States Wholesale Nursery
Mariosousa heterophylla on iNaturalist
ETHNOBOTANY
Palo blanco wood was often used by the Seri Indians of northern Mexico for building material because of this plant’s characteristically straight and minimally branched trunk.
NATURAL DISTRIBUTION
Mariosousa heterophylla is a sub-tropical native of Sonora, Mexico on hills, rocky slopes and canyons. There is another palo blanco from Baja California, Lysiloma candida, which is a bolder, thicker-trunked species and much more rare.
TAXONOMY AND NAME
This species is in the Fabaceae, the legume family. There are 14 accepted species in the genus Mariosousa restricted in range to Central America, Mexico, and the southwestern United States.
This plant was formerly known as Acacia willardiana and is often still sold under that name. Recently changed from Mariosousa willardiana to M. heterophylla. Mariosousa honors Mario Sousa, former Director of the Herbarium of the Instituto de Biología (MEXU), Universidad Autónoma de Mexico, who has done extensive work in Acacia systematics, and heterophylla means “different leaf” probably referring to the very unusual leaves of willow acacia.
Plants in the wild are almost always multi-trunked even though they grow straight up, rather than spreading like most of our native trees grow. Photo by Eric Hough, iNaturalist
Plants naturally grow in rocky hillsides in Sonora in full sun. Their white trunks reflect the intense sunlight and prevent sun scald. Photo by Sue Carnahan, iNaturalist
When palo blancos get to be a certain age, their bark peels back to reveal a glossy white trunk. Photo by Sue Carnahan, iNaturalist
White, rod-shaped catkins appear in spring followed by seed pods. Photo by Bodo Nuñez Oberg, iNaturalist
Seed pods start to drop in summer. Photo by Mike Plagens, iNaturalist