His 1942 study of the plants of the Río Mayo region of northwestern Mexico became a classic for the extent of its coverage of a previously little-known area.
In addition to purely botanical work, he was interested in ethnobotany, and his plant descriptions include information about their uses by indigenous peoples.
Works
Río Mayo Plants of Sonora-Chihuahua (1942), later updated posthumously as Gentry's Rio Mayo Plants (University of Arizona Press, 1998) ISBN0-8165-1726-6
The Agave Family of Sonora (USDA, 1972)
The Agaves of Baja California (California Academy of Sciences, 1978)
Agaves of Continental North America (University of Arizona Press, 1982) ISBN0-8165-2395-9
Cunningham, Isabel S. "Howard Scott Gentry: agriculture's renaissance man." Diversity 11 (1987): 23–24.
Erickson, Jim. "Botanist, agave expert Howard S. Gentry dies." The Arizona Daily Star (April 3, 1993).
"Famed plant researcher Howard Gentry at age 89" The Press Enterprise (April 8, 1993).
Hadley, Diana. "'Listening to my mind': Howard Scott Gentry's Recollections of the Rio Mayo." Journal of the Southwest 37 no. 2 (1995): 178–245.
Pierce, Alison. "The Mexican Apprenticeship: an authority on century plants became so while surviving rebellious Yaquis, bushwhackers and suspicious opium growers." Arizona (February 11, 1979): 40–46.
"Plant explorer honored by UA, industry and friends." Agri-News 9, no. 2 (July 1990).
Verbiscar, Anthony J. "Howard Scott Gentry December 10, 1903-April 1, 1993." Economic Botany 47, No.. 3 (1993).
Walters, James E. "Seeking answers in the desert." Saturday Magazine of the Scottsdale Daily Progress (March 2, 1985): 6–7.