It was named for its collector Josiah Gregg, who found the plant in 1847 at the site of the Battle of Buena Vista in the state of Coahuila, in northern Mexico during the Mexican-American War by Asa Gray of Harvard University in 1853. 
This shrub grows erect to nearly 2 m (6.6 ft) in maximum height. Its woody parts are gray in color and somewhat woolly. The evergreen leaves are oppositely arranged and variable in shape. They may be toothed or smooth along the edges. The inflorescence is a small cluster of many white flowers. It blooms in spring. The fruit is a horned capsule a few millimeters wide which bursts explosively to expel the three seeds which require thermal scarification from wildfire before they can germinate.
- Blakely, Larry, Desert Ceanothus, Ceanothus greggii A. Gray var. vestitus (E. Greene) McMinn (Rhamnaceae), Who's in a Name? People Commemorated in Eastern Sierra Plant Names
- Forest Service Fire Ecology
Media related to Ceanothus greggii at Wikimedia Commons
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