Species/taxon description: Tree to 10 m (30 ft), branches erect and sometimes numerous, 9-13 ribs, 8-10 cm (3.1-3.9 in) diameter, dark green to gray-green. Areoles pubescent, spines 13-20 per areole, up to 2.5 cm (1.0 in) long, usually less. Flowers solitary, 5-6 cm (2.0-2.4 in) long, campanulate, sepals ovate, outer petals green, inner petals white, 1-1.5 cm (0.4-0.6 in). Flowers open in the late afternoon or evening and smell like garlic. Berry depressed, reddish, +3.5 cm (1.4 in) diameter. Seeds black, shiny. (Ward 1978, Long & Lakela 1971)
Pilosocereus robinii has a history of confusing taxonomy. Long & Lakela (1971) name two varieties, robinii, and deeringii, the former of which was much more branched. Ward (1979) reported that variety robinii was extirpated during WWI. Confusingly, Benson (1982) says var. deeringii may be extirpated, but var. robinii can be found in the Keys. However Austin (1984), as well as Adams and Lima (1984) doubt there are really two varieties, stating that the less branched form may be an artifact of hurricanes and windier localities. Note that Anderson (2001) lumps this taxon into P. polygonus, along with P. bahamensis. Legal Status: Federally endangered. Florida endangered.
Conservation status: Native.
Prepared by: Conservation of South Florida Endangered and Threatened Flora (ETFLORA) Project, Research Department, Fairchild Tropical Garden
Last Updated: June 2008
Background and Current Status
Range-wide distribution – past and present
Population and reproductive biology/life history
Pollinators: Unknown. Possibly bats in Cuba or a sphingid moth in Florida (Adams & Lima 1994).
Flowering Period: Flower year round, peaking in July, August and September (Adams & Lima 1994). Bloom at night.
Fruiting: Fruit are mature + 30 days post pollination (Adams & Lima 1994). Of 32 buds that were tagged and followed, Adams (1996?) found that only 22% set mature fruit; the majority of buds fell to the ground while still immature.
Germination Requirements: fresh seed can germinate readily, 1 min soak in 1N H2SO4 resulted in 95% germination (81% no treatment, 85% 5 min soak) in seeds that were stored in ambient conditions for approx. 4 months (Walters, unpublished data)
Establishment Requirements: unknown
Population Size: (Confidential)
Annual Variation: unknown
Number and Distribution of Populations: (Confidential)
Acanthocereus tetragonus is common. (ETFLORA 2007)
Animal use: Frugivory, predation of seeds by ants (Adams & Lima 1994)
Herbivory and/or use of trunks for antler polishing by Key Deer
Fire: Fire is rare in hardwood hammocks, but it has the potential to devastate a
population of P. robinii (USFWS 1986).
Hurricane: Probably reduce branches (Austin 1984). Blow-downs and storm surge can devastate populations.
Slope Movement: unknown
Small Scale (i.e. Animal Digging): unknown
Protection and management
Summary: The majority of the remaining P. robinii plants are on protected land. They are not actively managed due to difficulty of access and lack of information as to how best manage for this species.
Availability of source for outplanting: There are ex-situ collections Fairchild and at the Desert Botanical Garden (Phoenix, AZ).
Availability of habitat for outplanting: (Confidential)
Herbivory: Possible herbivory by Key Deer and small mammals.
Disease: The fungal pathogen Botryodiplodia sp. was isolated (by the FL Dept.
Hurricane: Salt water incursion from hurricane storm surge has likely been a
major factor in the recent decline, possibly exacerbated by altered hydrology
caused by digging of mosquito ditches in one hammock (ETFLORA 2007). Probably reduce branches (Austin 1984).
On site: Urban development has been the worst threat (Ward 1979, USFWS
1986, Adams and Lima 1994, Adams 1996?). Poaching is also a danger (USFWS
1986). As early as 1917, Small wrote that many individuals were destroyed from development and harvesting of hammock trees for firewood. Some reached 20 feet high, and he “counted a score of prostrate skeleton remains scattered over the hammock floor which were either cut down by wood hunters or blown down by storms.”
Off site: unknown
The Institute for Regional Conservation
USFWS, Key Deer National Wildlife Refuge
Conservation measures and actions required
Research history: Autecological research on this taxon was conducted in the 1990s by Ralph Adams and Alex Lima. Their studies (cited below) included reproduction, distribution, and natural history. Dr. Peter Stiling of the University of South Florida may have done minor research into this species (Bill Seese, Key Deer NWR, pers. comm.). Phil Frank of NWR has GIS maps of the population within the Refuge’s boundaries. Fairchild mapped all but one population in 2006-2007 and has ongoing research to determine the cause for the recent population decline and to identify optimal habitat characteristics. We have also expanded the ex-situ collections including rescuing cuttings from dying plants and are evaluating potential reintroduction sites.
Significance/Potential for anthropogenic use: None, other than interest to cacti enthusiasts/collectors.
Recovery objectives and criteria: The USFWS (1986) recovery plan objective is to “restore the Key tree-cactus to a stable, secure and self-sustaining status allowing removal of the species from protection under the Endangered Species Act.” Criteria include protection of existing populations from vandalism, collection, and habitat destruction; proper management; research into the ecology, demography, and reproductive biology; feasibility studies for reintroduction; conservation of germplasm; and assessment of the status of the population(s) in Cuba.
Management options: Monitoring by ETFLORA in 2001-2002 indicated that Pilosocereus robinii was declining health in the wild. Surveys conducted in 2006-2007 revealed a substantial decline, particularly in the largest population. In addition to the management recommendations detailed in the USFWS Recovery Plan (1986) described above, more extensive monitoring is recommended. Analysis of dead cactus tissue by the Florida Dept. of Agriculture and Consumer Services, Division of Plant Industry in Gainesville, FL may be in order.
Next Steps: Regular monitoring and rescue of dying plants if more are found.
Propagation and reintroduction.
Seed ecology studies if permitted by USFWS.
Population genetics study to determine amount of genetic diversity within and among populations if permitted by USFWS.
Acquisition of private lands where Key Tree Cactus is located if possible to protect them from development.
Adams, R.M. 1996? The sexual reproductive potential of the Florida Keys tree-cactus, Pilosocereus robinii. Final report, agency unknown (on file at Fairchild Tropical Garden).
Adams, R.M. and A.N. Lima. 1994. The natural history of the Florida Keys tree cactus, Pilosocereus robinii. Report to USFWS.
Anderson, E.F. 2001. The cactus family. Timber Press, Portland Oregon.
Austin, D.F. 1984. Resume of the Florida taxa of Cereus (Cactaceae). Florida Scientist 47(1):68-72.
Benson, L. 1982. The cacti of the United States and Canada. Stanford University Press, Stanford, CA.
Byles, R.S. and G.D. Rowley. 1957. Pilosocereus Byl. & Rowl. nom. gen. nov. (Cactaceae). The cactus and succulent journal of Great Britain 19:66-69.
Long, R.W. and O. Lakela. 1971. A flora of tropical Florida: A manual of the seed plants and ferns of southern peninsular Florida. University of Miami Press, Coral Gables, FL. 962 pp.
Mace, T. 1974. The genus Pilosocereus. 1. Natl cac suc j. 29(1):18.
Small, J.K. 1917. The tree cacti of the Florida Keys. Journal of the New York Botanical Garden 18(213):199-203.
Snyder, J.R., A. Herndon and W.B. Robertson. 1990. South Florida Rockland. In Myers, R.L. and J.J. Ewel, eds. Ecosystems of Florida. University of Central Florida Press, Orlando. 765 pp.
USFWS. 1986. Key tree-cactus (Cereus robinii) recovery plan. U.S. Department of the Interior, Fish and Wildlife Service, Southeast Region, Atlanta, Georgia.
Ward, D.B. 1979. Rare and endangered biota of Florida. P.C.H. Pritchard, series editor. Plants. Vol 5. University Presses of Florida, Gainesville, Florida.