CPC Plant Profile: Key Tree Cactus
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Plant Profile

Key Tree Cactus (Pilosocereus robinii)

The multiple spiny stems of the Key tree cactus. Photo Credit: Lippincott
Description
  • Global Rank: G1 - Critically Imperiled
  • Legal Status: Federally Endangered
  • Family: Cactaceae
  • State: FL
  • Nature Serve ID: 142546
  • Date Inducted in National Collection: 03/14/1986

The keys tree cactus is unlike any other plant in Florida. It is a true tree, with mature individuals possessing differentiated trunks and branches (Avery 1982). Plants can reach as high as 10 m, and may have dozens of spreading branches (Ward 1979), though most of the larger plants have been destroyed by development and hurricanes (USFWS 1986). The showy, 6 cm-long flowers are reported to smell like garlic (Hennesey and Habeck 1994). Although first discovered in the early 1800s, this species was very little studied until 75 years later (Small 1917), due in part to both its isolation from civilization and the awkwardness of making herbarium specimens of such a large cactus.

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Updates
  • 09/23/2020
  • Propagation Research

Seed viability was 57.7% (N=6397) and fruit set was 21.9% (N=32) in laboratory trials (Adams, undated report). It has not been determined with certainty whether the two apparent forms of the Keys tree cactus are genetically nondistinct. If an outplanting were to take place, seeds need to be collected and used to propagate seedlings for outplanting.

  • 09/23/2020
  • Reproductive Research

Reproduction: The Keys tree cactus flowers year round, peaking in July, August and September. Flowers bloom (and smell garlicky) at night (Hennessey and Habeck 1994). Seed viability was 57.7% (N=6397) and fruit set was 21.9% (N=32) in laboratory trials (Adams, undated report). Natural History: Information on population age class, growth rates, and architecture is contained in Adams and Lima (1994). Dr. Peter Stiling, of the University of South Florida, may be continuing natural history research. Predation: Adams and Lima (1994) noted ants and cardinals predating on the seeds and fruit, respectively. Hennessey, M. K. and D. H. Habeck (1994). ""Observations on reproduction of an endangered cactus, Cereus robinii (Lemaire) L. Benson."" Florida Scientist 57: 93-101. This rare cactus is subjected to mosquito insecticide spraying which has an unknown effect on its pollinators. No pollinators were observed, so cross pollination by animals remains unconfirmed. Its floral biology strongly suggests pollination by bats or moths. Pesticide spraying could have impacts on its reproductive cycle.

Nature Serve Biotics
  • 05/02/2017

Known from the Florida Keys and Cuba and rare throughout its range, with only 7 occurrences believed extant in the United States. Since the mid-1990s, significant declines have been observed at the Florida Keys sites. The species is subject to cactus collection and its limited habitat is disappearing rapidly due to encroaching development and agricultural conversion; only a few of the occurrences are formally protected. It is also threatened by increasing soil salinity due to sea level rise and storm surge; hurricanes are also occassionally destructive to the few populations. Sea level and storm impacts are predicted to worsen as climate change proceeds, especially given that there is limited connectivity between this species' habitat and higher ground.

Jennifer Possley
  • 01/01/2010

Known threats include habitat destruction and hurricanes (the latter of which limit size, but probably not reproduction) (USFWS 1986). Other possible threats include canopy closure, salt water intrusion, drainage, competition, and accumulation of soil

Jennifer Possley
  • 01/01/2010

Populations: 9 in Florida (FNAI 1998), 1 unconfirmed in Cuba (Adams, undated report) Individuals: 624 in the Keys (Adams and Lima 1994), and an unknown number in Cuba

Jennifer Possley
  • 01/01/2010

Reproduction: The Keys tree cactus flowers year round, peaking in July, August and September. Flowers bloom (and smell garlicky) at night (Hennessey and Habeck 1994). Seed viability was 57.7% (N=6397) and fruit set was 21.9% (N=32) in laboratory trials (Adams, undated report). Natural History: Information on population age class, growth rates, and architecture is contained in Adams and Lima (1994). Dr. Peter Stiling, of the University of South Florida, may be continuing natural history research. Predation: Adams and Lima (1994) noted ants and cardinals predating on the seeds and fruit, respectively. Hennessey, M. K. and D. H. Habeck (1994). ""Observations on reproduction of an endangered cactus, Cereus robinii (Lemaire) L. Benson."" Florida Scientist 57: 93-101. This rare cactus is subjected to mosquito insecticide spraying which has an unknown effect on its pollinators. No pollinators were observed, so cross pollination by animals remains unconfirmed. Its floral biology strongly suggests pollination by bats or moths. Pesticide spraying could have impacts on its reproductive cycle.

Jennifer Possley
  • 01/01/2010

Responsible Agencies: Florida Department of Environmental Protection, Florida Keys National Wildlife Refuge, U.S. Fish and Wildlife Service, private landowners. The National Wildlife Refuge and USFWS protect the land containing the largest population of the Keys tree cactus, but they do not regularly monitor the population. FDEP conducts periodic monitoring of the populations on its lands.

Jennifer Possley
  • 01/01/2010

A regular monitoring schedule on Federal lands. A clear summary of the status of the Keys tree cactus on private lands. Outplanting of the cactus onto sites where it currently or historically is/was found. Research on the effects of light levels, salt water, organic matter or competition.

Jennifer Possley
  • 01/01/2010

It has not been determined with certainty whether the two apparent forms of the Keys tree cactus are genetically nondistinct. If an outplanting were to take place, seeds need to be collected and used to propagate seedlings for outplanting.

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Nomenclature
Taxon Pilosocereus robinii
Authority (Lemaire) Byles and Rowley
Family Cactaceae
CPC Number 15862
ITIS 504398
USDA PIRO5
Common Names Key tree cactus | Keys tree cactus
Associated Scientific Names Pilosocereus robinii var. robinii | Cereus robinii | Pilosocereus robinii | Cereus robinii var. keyensis | Pilocereus deeringii | Pilosocereus deeringii | Pilosocereus robinii var. deeringii
Distribution The Florida Keys and Cuba (USFWS 1986).
State Rank
State State Rank
Florida S1
Habitat

Rocky tropical hardwood hammocks (USFWS 1986)

Ecological Relationships

Pollinators are unknown, but Adams and Lima (1994) theorize it must be a sphingid moth, since no other insects capable of pollinating the large flowers were seen at the site, and no nectar feeding bats are native to the Keys.

Pollinators
Common Name Name in Text Association Type Source InteractionID
Reintroduction
Lead Institution State Reintroduction Type Year of First Outplanting
Fairchild Tropical Botanical Garden Florida Reintroduction 2012
Fairchild Tropical Botanical Garden Florida Reintroduction 2015
Fairchild Tropical Botanical Garden Florida 2021
Fairchild Tropical Botanical Garden Florida 2021
Fairchild Tropical Botanical Garden Florida Reinforcement 2021
Fairchild Tropical Botanical Garden Florida Reinforcement 2021
Fairchild Tropical Botanical Garden Florida Reinforcement 2022
Fairchild Tropical Botanical Garden Florida Reinforcement 2022

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