Research and Conservation in Southern Sonora, Mexico

Ipomoea arborescens (Humb. & Bonpl. ex Willd.) G. Don var. arborescens
(palo santo, palo blanco, tree morning glory)

Tree morning glory is a common species in the tropical forests of southern Sonora. It ranges from northern Sonora southward into Michoacán and Morelos. The fast-growing plants (2-3 meters/year) produce soft semisucculent stems. They are in leaf only during the brief summer rainy season. Foliage is shed soon after the rain stops in September, and flowering occurs from November to March.

A tree morning glory in leaf during the summer rainy season. Photo: Mark Dimmitt	Leafless tree in flower in winter. Photo: Stephanie A. Meyer
Flower of Ipomoea arborescens arborescens. The clear yellow-green throat is diagnostic of the variety; there may be some purple spots. Photo: Mark Dimmitt

Ipomoea arborescens var. pachylutea Gentry
(palo santo amarillo)

This variety occurs at higher elevations than var. arborescens, at the transition between tropical deciduous forest and oak woodland. It differs from the nominate variety in having a yellowish bark and harder wood, much larger and hairier leaves, and dark purple flower throats.

Ipomoea arborescens pachylutea near Alamos, Sonora in the dry season. Photo: Mark Dimmitt	Ipomoea arborescens pachylutea near Alamos, Sonora in summer. Photo: Martín G. Figueroa
I. arborescens pachylutea flower. Note the dark throat. Photo: Mark Dimmitt	Bark of Ipomoea arborescens pachylutea. Photo: Mark Dimmitt
I. a. pachylutea (foreground) and var. arborescens grown side-by-side in Tucson. The former has larger leaves and yellowish bark. Photo: Mark Dimmitt

The flowers of tree morning glories are major nectar sources for lesser long-nosed bats, hummingbirds, and probably bees. Deer feed on the abundant fallen flowers.

Reference

Austin, Daniel F., Richard S. Felger, & Thomas R. Van Devender. 2005. Nomenclature of Ipomoea arborescens (Convolvulaceae) in Sonora, Mexico. Sida 21(3)1283-1292.