CPC National Collection Plant Profile

Manihot walkerae

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CPC National Collection Plant Profile

Manihot walkerae


Family: 
Euphorbiaceae  
Common Names: 
Walker's manihot, Walker's manioc
Author: 
Croizat
Growth Habit: 
Forb/herb
CPC Number: 
2798

Distribution
Protection
Conservation
References


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Manihot walkeraeenlarge
Image Owner: San Antonio Botanical Garden

Manihot walkeraeenlarge
Image Owner: San Antonio Botanical Garden


Manihot walkerae is Fully Sponsored
Primary custodian for this plant in the CPC National Collection of Endangered Plants is: 
Cindy Barrett contributed to this Plant Profile.

 
Manihot walkerae


Manihot walkerae is an endangered plant in South Texas and parts of Mexico (USFWS 1993). It is related to other Manihot species which are grown in Third World countries in order to provide cassava, an important source of starch for millions of people. The roots must first be boiled in order to extract poisonous, possibly fatal, acids. Tapioca is a product derived from cassava. Manihot walkerae is the most cold hardy of the Manihots. Crossing this species with others may increase the growing range of those Manihots used as a food source. Manihot walkerae may also contain important disease resistant genes. (USFWS 1993).

Separate female and male flowers occur on the same plant, with all flowers blooming from April to September following rain. Male flowers occur on elongated stems and are white with light purple streaks. They have five lobes, are nearly 1/2 inch long, and are shaped as tubes. Female flowers, much smaller than male flowers at only 3/8 of an in long, occur at the base of the long stalks of the male flowers. (Texas Parks and Wildlife 2002)

Distribution & Occurrence

State Range
  Texas
State Range of  Manihot walkerae
Habitat
  Found in the Tamaulipan Biotoic province, on mesic upland in or near dense stands of native brush, which create a microclimate of shade, protection from trampling/grazing, and lower temperatures,.

Distribution
  Known from the Lower Rio Grande Valley of Texas (Hidalgo and Starr counties) and northern Tamaulipas, Mexico. (Texas Parks and Wildlife 2002)

Number Left
  • Found in four locations in Hidalgo and Starr Counties in Texas. One is located on private land, and contains only one plant, the other three are located in the Lower Rio Grande National Wildlife Refuge. (Texas Parks and Wildlife 2002)
• Two populations are known from northern Tamaulipas, Mexico. (USFWS 1993)

Protection

Global Rank:  
G1
 
9/4/1996
Guide to Global Ranks
Federal Status:  
LE
 
10/24/1996
Guide to Federal Status
Recovery Plan:  
Yes
 

State/Area Protection
  State/Area Rank Status Date  
  Mexico *FR83 8/26/1988  
  Texas S1 10/8/1991  

Conservation, Ecology & Research

Ecological Relationships
  • As there are so few populations of Manihot walkerae, little is known of its ecological relationships. (USFWS 1993).
• Separate male and female flowers occur on the same plant--the single plant in Hidalgo County, Texas, has produced seed, so the species is hypothesized to be self-fertile. However, the flowers are reportedly fragrant. Possible pollinators are unknown. (Texas Parks and Wildlife 2002)

Threats
  The major threat to Walker’s manioc is the destruction and fragmentation of native brush and grassland habitats where it is currently found. As of 1993, when the recovery plan for this species was written, it was estimated that over 95% of the habitat that this species might occupy on the U.S. side of the border in southern Texas has been destroyed for agricultural, urban, and recreational use. The remaining 5% of native habitat that remains occurs primarily in small fragments, which are increasingly vulnerable to further destruction. (USFWS 1993)

Current Research Summary
  The San Antonio Botanical Garden conducted a germination study using an environmental growth chamber at Trinity University. Treatments included heat stratification, as well as, mechanical and acid scarification. For the first time, Manihot seeds germinated under cultivation, giving insight into breaking seed dormancy through heat stratification. Also, Chris Best at the U.S. Fish and Wildlife Service's Santa Ana Wildlife Refuge has investigated the effects of using mechanical and chemical scarification, aeration, seed storage time, and growth regulators.

Current Management Summary
  Walker’s manioc has been under cultivation at the University of Texas at Austin (UT-Austin) since 1940. Currently the San Antonio Botanical Garden maintains a core collection of Manihot walkerae from plants at UT-Austin in a cold frame and greenhouse. Some plants were planted into a test plot and demonstration garden for both research and educational reasons. Seed from core collection plants are being stored on site for research. In cooperation with the U.S. Fish and Wildlife Service, Manihot plants and habitat existing on U.S. sites are being voluntarily protected by private landowners. Mexico populations are being monitored by a Mexican botanist, Fransisco Gonzalez Medrano, under a U.S.-Mexico cooperative agreement with the U.S. Fish and Wildlife Service. (USFWS 1993)

Research Management Needs
  • Monitoring and surveys
• Pollination biology
• Response to disturbance
• Seed dispersal and seedling recruitment
• Habitat characterization
• Genetic analysis
• Germination requirements

Ex Situ Needs
  See above.

References

Books (Single Authors)

Correll, D.S.; Johnston, M.C. 1970. Manual of the vascular plants of Texas. Renner: Texas Research Foundation. 1881p.

Rogers, D.J.; Appan, S.G. 1973. Flora Neotropica, Monograph No. 13. Manihot [and] Manihotoides (Euphorbiaceae). New York: Hafner Press.

Books (Sections)

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.

Electronic Sources

(2002). Texas Threatened and Endangered Plants--Profiles. Texas Parks and Wildlife. http://www.tpwd.state.tx.us/nature/endang/plants/index.htm. Accessed: 2002.

(2002). Threatened and Endangered Species Profiles. Texas Parks and Wildlife. http://www.tpwd.state.tx.us/publications/wildlife_habitat/species_profiles/plants/index.htm. Accessed: 2002.

Journal Articles

Croizat, L. 1942. New and critical Euphorbiaceae chiefly from the Southeastern United States. Bulletin of the Torrey Botanical Club. 69, 6: 445-460.

Ideker, J. 1990. Manihot walkerae rediscovered. The Sabal. 7, 8: 1-2.

USFWS. 1976. Proposed Endangered Status for 1700 U.S. Plants. Federal Register. 41: 24523-24572.

USFWS. 1991. Final Rule to List the Plant Manihot walkerae as Endangered. Federal Register. 56, 191: 49850-49854.

Reports

Clayton, P.W. 1990. Summary of Field Work on WalkerÆs Manioc. Corpus Christi,; TX: U.S. Fish and Wildlife Service, Corpus Christi Ecological; Services.

Gulick, P.; Hershey, C.; Esquinas-Alcazar. 1983. Genetic resource of cassava and wild relatives. Rome, Italy: International Board for Plant Genetic Resources.

Jahrsdoerfer, S.E.; Leslie, D.M., Jr. 1988. Tamaulipan brushland of the Lower Rio Grande Valley of south Texas: description, human impacts, and management options. U.S. Fish & Wildlife Service Biological Report. p.63. Report number 88(36).

Turner, B.L. 1982. Status Report: Manihot walkerae Croizat. Albuquerque, NM: U.S. Fish and Wildlife Service. p.9.

USFWS. 1993. Walker's manioc (Manihot walkerae) recovery plan. Albuquerque, New Mexico: U.S. Fish and Wildlife Service, Region 2. p.57.


  This profile was updated on 3/4/2010
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