Family: Cactaceae
Common Name: Thornber’s fishhook cactus

Mamillaria thornberi is a small, clumping columnar cactus with a soft body and numerous tubercules without dorsal grooves (as in Coryphantha). The stems are approximately 15 cm high, and ca 2 cm in diameter. Each tubercule has 10-20 straw-colored radial spines, and a single darker large hooked central spine-hence the name ‘fishook cactus’ (Benson 1982). Pinkish-white flowers bloom sporadically, usually following heavy rains. Flowers form in a ring around the upper portion of the stem, but not at the apex. The edible fruits are bright red, fleshy, ca. 2 cm long, and shaped like little chili-peppers.

Species in the genus Mammillaria often go through “boom and bust” population cycles. This species is a good example of that, as it occurred in the millions in the Avra Valley west of Tucson in the 1930’s, but most of the population disappeared in a catastrophic freeze in 1937. The population never recovered, and the species was considered for federal threatened status in the mid-1980’s.

Habitat

The microhabitat preferred by M. thornberi is the area beneath the overhanging side branches of Ambrosia dumosa (Rutman 1995). In order to find plants, one must lift these branches up to inspect the area beneath each Ambrosia plant, an onerous task as Ambrosia dumosa is highly abundant in southern Arizona.

Distribution

South-central Arizona.

There are eight major populations, with only 2 sites on protected lands. The majority of other populations are found on the Tohono O’odham, and the San Xavier reservations, and on private land (Rutman 1995).

References

Books

Benson, L. 1982. The Cacti of the United States and Canada. Stanford, California: Stanford University Press. 1044p.

Kartesz, J.T. 1993. Species distribution data for vascular plants of 70 geographical areas, from unpublished data files at the North Carolina Botanical Garden.

Kartesz, J.T. 1996. Species distribution data at state and province level for vascular plant taxa of the United States, Canada, and Greenland (accepted records), from unpublished data files at the North Carolina Botanical Garden.

Kartesz, J.T. 1999. A synonymized checklist of the vascular flora of the U.S., Canada, and Greenland. In: Kartesz, J.T.; Meacham, C.A., editors. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden. Chapel Hill, NC.

Journal Articles

1984. Endangered Species. AABGA Newsletter. pp. 5.

Nabhan, G.; Gass, V.; Quirk, P. 1986. Thornber’s Fishook Cactus: conserving a declining species. Agave. 2, 2: 4-8.

Thomas, P.A.; Goodson, P. 1992. Conservation of succulents in desert grasslands managed by fire. Biological Conservation. 60, 2: 91-100.

USFWS. 1984. Carex specuicola. Endangered Species Technical Bulletin. 9, 5: 11.

USFWS. 1984. Four Western Plants. Endangered Species Technical Bulletin. 9, 5: 8-9.

USFWS. 1984. Proposal to Determine Mammillaria thornberi (Thornber’s Fishhook Cactus) to be a Threatened Species. Federal Register. 49, 80: 17551-17553.

USFWS. 1985. Notice of Six-Month Extension on the Proposed Rule for Mammillaria thornberi (Thornber’s Fishhook Cactus). Federal Register. 50, 111: 24241-24242.

USFWS. 1988. Regional News–Region 2. Endangered Species Technical Bulletin. 13, 11-12: 3.

Reports

McLaughlin, S. 1987. Salvage, propagation and re-establishment of Mamillaria thornberi. Tucson, Arizona: Progress report: Tucson Water.

McLaughlin, S. 1988. Salvage, propagation and re-establishment of Mamillaria thornberi. Tucson, Arizona: Progress report: Tucson Water.

Rutman, S. 1995. The distribution of Mamillaria thornberi on Saguaro National Monument, Tucson Mountain Unit, Arizona. Tucson, Arizona: Saguaro National Monument.

Ecker, Liz S. 1990. Population enhancement of a rare Arizona cactus, Mammillaria thornberi Orcutt (Cactaceae). [M.S. Thesis]: Arizona State University. 95p.