Manihot walkerae
Encyclopedia
Manihot walkerae, commonly known as Walker's Manihot, is a species of flowering plant
in the spurge family, Euphorbiaceae
, that is native to the Lower Rio Grande Valley
of Texas
in the United States
and Tamaulipas
in Mexico
. The specific name honours amateur botanist E. J. Walker, who discovered the type specimen near Mission
and La Joya, Texas
in 1942.
herb
or small shrub
that reaches a height of up to 0.5 m (1.6 ft). The entire plant has an odor resembling hydrogen cyanide. Root
s are carrot-shaped and tuber
ous, while stems are prostrate or ascending-erect. The peltate
leaves are alternate, simple, glabrous, 5–14 cm (2–5.5 in) long and 4–11 cm (1.6–4.3 in) wide. They are palmately lobed, with 3-5 pandurate to halberd-shaped lobes. The white flowers occur in androgynous, axillary, subspicate raceme
s. The fruit is a dehiscent
capsule
10–12 mm (0.393700787401575–0.47244094488189 in) in length.
. Soils are shallow, calcareous
sandy loam
s, often derived from the caliche
and conglomerate of the Goliad Formation. Associated woody plants include Acacia rigidula
, Citharexylum brachyanthum, Cylindropuntia leptocaulis
, Karwinskia humboldtiana
, Leucophyllum frutescens
, and Prosopis glandulosa. Walker's Manihot has been collected from the Loreto caliche sand plain in Tamaulipas, where it grew alongside Asclepias prostrata, Manfreda longiflora, and Physaria thamnophila.
on 2 October 1991 and the Texas Endangered Species List on 30 March 1993. NatureServe considers it critically imperiled, as the wild population is estimated to be less than 1,000 plants. Protected populations occur in the Lower Rio Grande Valley National Wildlife Refuge
, while cultivated specimens exist at the San Antonio Botanical Garden
, the University of Texas at Austin
, and Santa Ana National Wildlife Refuge
.
(M. esculenta) and has been studied for its role in introducing valuable traits into the latter. The tubers of M. walkerae exhibit dramatically delayed postharvest physiological deterioration (PPD). This trait can be passed to M. esculenta × M. walkerae hybrids, allowing the roots to remain intact 1 month after harvest.
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
in the spurge family, Euphorbiaceae
Euphorbiaceae
Euphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....
, that is native to the Lower Rio Grande Valley
Rio Grande Valley
The Rio Grande Valley or the Lower Rio Grande Valley, informally called The Valley, is an area located in the southernmost tip of South Texas...
of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Tamaulipas
Tamaulipas
Tamaulipas officially Estado Libre y Soberano de Tamaulipas is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 43 municipalities and its capital city is Ciudad Victoria. The capital city was named after Guadalupe Victoria, the...
in Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. The specific name honours amateur botanist E. J. Walker, who discovered the type specimen near Mission
Mission, Texas
Mission is a city in Hidalgo County, Texas, United States. The population was 77,058 at the 2010 census Mission is part of the McAllen–Edinburg–Mission and Reynosa–McAllen metropolitan areas.-Geography:Mission is located at ....
and La Joya, Texas
La Joya, Texas
La Joya is a city in western Hidalgo County, Texas, United States, along U.S. Route 83 between Mission and Rio Grande City. The population was 3,985 at the 2010 census.La Joya is part of the McAllen–Edinburg–Mission and Reynosa–McAllen metropolitan areas....
in 1942.
Description
M. walkerae is a perennialPerennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
herb
Herbaceous plant
A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
or small shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
that reaches a height of up to 0.5 m (1.6 ft). The entire plant has an odor resembling hydrogen cyanide. Root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s are carrot-shaped and tuber
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
ous, while stems are prostrate or ascending-erect. The peltate
Leaf shape
In botany, leaf shape is characterised with the following terms :* Acicular : Slender and pointed, needle-like* Acuminate : Tapering to a long point...
leaves are alternate, simple, glabrous, 5–14 cm (2–5.5 in) long and 4–11 cm (1.6–4.3 in) wide. They are palmately lobed, with 3-5 pandurate to halberd-shaped lobes. The white flowers occur in androgynous, axillary, subspicate raceme
Raceme
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
s. The fruit is a dehiscent
Dehiscence (botany)
Dehiscence is the opening, at maturity, in a pre-defined way, of a plant structure, such as a fruit, anther, or sporangium, to release its contents. Sometimes this involves the complete detachment of a part. Structures that open in this way are said to be dehiscent...
capsule
Capsule (fruit)
In botany a capsule is a type of simple, dry fruit produced by many species of flowering plants. A capsule is a structure composed of two or more carpels that in most cases is dehiscent, i.e. at maturity, it splits apart to release the seeds within. A few capsules are indehiscent, for example...
10–12 mm (0.393700787401575–0.47244094488189 in) in length.
Habitat
Walker's Manihot generally grows under the branches of larger shrubs and trees. In Texas, this species inhabits xeric slopes and uplands in thorny shrublandsTamaulipan mezquital
The Tamaulipan mezquital ecoregion, in the deserts and xeric shrublands biome, is located in the southern United States and northeastern Mexico...
. Soils are shallow, calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
sandy loam
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...
s, often derived from the caliche
Caliche
Caliche may refer to:*Caliche, a hardened deposit of calcium carbonate.*Caliche slang, a collection of slang words unique to Salvadoran Spanish....
and conglomerate of the Goliad Formation. Associated woody plants include Acacia rigidula
Acacia rigidula
Acacia rigidula, commonly known as Blackbrush Acacia or Chaparro Prieto, is a species of shrub or small tree in the legume family, Fabaceae. Its native range stretches from Texas in the United States south to central Mexico. This perennial is closely related to A. berlandieri and is not listed as...
, Citharexylum brachyanthum, Cylindropuntia leptocaulis
Cylindropuntia leptocaulis
Cylindropuntia leptocaulis, Desert Christmas cactus, Desert Christmas Cholla, and Tasajillo, is a cactus.-Distribution:...
, Karwinskia humboldtiana
Karwinskia humboldtiana
Karwinskia humboldtiana, commonly known as Coyotillio or Humboldt Coyotillo, is a species of flowering shrub or small tree in the buckthorn family, Rhamnaceae. It is native southern and western Texas in the United States as well as much of Mexico...
, Leucophyllum frutescens
Leucophyllum frutescens
Leucophyllum frutescens is an evergreen shrub in the figwort family, Scrophulariaceae, native to the state of Texas in the southwestern United States and the states of Coahuila, Nuevo León, and Tamaulipas in northern Mexico. Although commonly known as Texas Sage, it is not a true sage and is...
, and Prosopis glandulosa. Walker's Manihot has been collected from the Loreto caliche sand plain in Tamaulipas, where it grew alongside Asclepias prostrata, Manfreda longiflora, and Physaria thamnophila.
Conservation
M. walkerae was added to the United States Endangered Species ListEndangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...
on 2 October 1991 and the Texas Endangered Species List on 30 March 1993. NatureServe considers it critically imperiled, as the wild population is estimated to be less than 1,000 plants. Protected populations occur in the Lower Rio Grande Valley National Wildlife Refuge
Lower Rio Grande Valley National Wildlife Refuge
The Lower Rio Grande Valley National Wildlife Refuge is a National Wildlife Refuge in Texas.Here, on the international border between the United States and Mexico, a host of nature's borders converge - climate, community, land form and geography...
, while cultivated specimens exist at the San Antonio Botanical Garden
San Antonio Botanical Garden
The San Antonio Botanical Garden is a , non-profit botanical garden in San Antonio, Texas.The garden was first conceived in the 1940s by Mrs. R. R. Witt and Mrs. Joseph Murphy, who organized the San Antonio Garden Center. The two went on to develop a master plan for a city botanical center in the...
, the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
, and Santa Ana National Wildlife Refuge
Santa Ana National Wildlife Refuge
Santa Ana National Wildlife Refuge is a refuge situated along the banks of the Rio Grande in Hidalgo County, Texas south of Alamo, Texas. It was established for the protection of migratory birds in 1943...
.
Uses
Walker's Manihot is a close relative of the widely cultivated cassavaCassava
Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...
(M. esculenta) and has been studied for its role in introducing valuable traits into the latter. The tubers of M. walkerae exhibit dramatically delayed postharvest physiological deterioration (PPD). This trait can be passed to M. esculenta × M. walkerae hybrids, allowing the roots to remain intact 1 month after harvest.