"Yerba is Spanish for herb, and thus one would think that mansa is also from Spanish as well, but all indications point to the fact that it is not. Mansa means calm or tranquil in Spanish, and the plant has no sedative effect, nor did local people ever use it as a calming agent. Its primary use is as an antimicrobial, antibacterial, and antifungal.
The most likely explanation is that mansa is a Spanish alteration of the original native word for the plant, now lost in the depths of time. . ."
Quoted here by permission of the author:
[Soule, J. A. 2011. Father Kino's Herbs: Growing and Using Them Today. Tierra del Sol Press, Tucson, AZ.]
Perhaps there is some connection to the Manso Indians