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Plant Profile

Thornber's Fishhook Cactus (Mammillaria thornberi)

M. thornberi is found underneath the overhanging side branches of Ambrosia dumosa, making this small clumping cactus very difficult to find. Photo Credit: Lynda Pritchett-Kozak

Global Rank: G4 - Apparently Secure
Legal Status: N/A
Family: Cactaceae
State: AZ, MX, SI
Nature Serve ID: 128379
Lifeform: Shrub
Categories of Interest: Cacti/Succulents
Date Inducted in National Collection: 03/14/1986

Description:

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.

Where is Thornber's Fishhook Cactus (Mammillaria thornberi) located in the wild?

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

States & Provinces:

Thornber's Fishhook Cactus can be found in Arizona, Mexico, Sonora

Which CPC Partners conserve Thornber's Fishhook Cactus (Mammillaria thornberi)?

Desert Botanical Garden

Not Sponsored

Conservation Actions

Assigned 06/09/17

CPC's Plant Sponsorship Program provides long term stewardship of rare plants in our National Collection. We are so grateful for all our donors who have made the Plant Sponsorship Program so successful. We are in the process of acknowledging all our wonderful plant sponsorship donors on our website. This is a work in progress and will be updated regularly.

Conservation Actions

10/10/2020

Initial tests on seed that had been processed and frozen yielded percentages of approximately 30%, but tests conducted on desiccated seed stored at room temperature for 2 years resulted in 75% germination. Germination tests are in progress on seeds stored using a variety of storage methods.

10/10/2020

Additionally the Garden has at least 250,000 seeds produced in cultivation.

10/10/2020

Desert Botanical Garden has 110 accessioned plants which were salvaged from an area slated as right-of-way for the Central Arizona Project Canal, and 42 clones of the accessioned plants.

Nature Serve Biotics

05/02/2017

Small population size, about 600 plants in 2 population areas. Limited distribution increases the species vulner- ability to natural and man-made stresses.

Kathleen C. Rice

01/01/2010

Threats to M. thornberi include urban development and maintenance of the Central Arizona Project Canal (Nabhan et al. 1986).

Kathleen C. Rice

01/01/2010

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).

Kathleen C. Rice

01/01/2010

Desert Botanical Garden has 110 accessioned plants which were salvaged from an area slated as right-of-way for the Central Arizona Project Canal, and 42 clones of the accessioned plants. Additionally the Garden has at least 250,000 seeds produced in cultivation. Plants are prolific seed producers, fruiting as frequently as they flower. Initial tests on seed that had been processed and frozen yielded percentages of approximately 30%, but tests conducted on desiccated seed stored at room temperature for 2 years resulted in 75% germination. Germination tests are in progress on seeds stored using a variety of storage methods.

Kathleen C. Rice

01/01/2010

Habitat protection would aid in conserving this species. Understanding the impact of Ambrosia dumosa on the population dynamics of Mammillaria thornberi would be useful as would knowing this species general reproductive biology and ecology.