''Ambrosia cheiranthifolia'' is a rare species of flowering plant known by the common names South Texas ambrosia and Rio Grande ragweed. It is native to the coast of

South Texas South Texas is a region of the U.S. state of Texas that lies roughly south of—and includes—San Antonio. The southern and western boundary is the Rio Grande, and to the east it is the Gulf of Mexico. The population of this region is about 4.96 ...

and the Mexican states of

Tamaulipas Tamaulipas (), officially the Free and Sovereign State of Tamaulipas ( es, Estado Libre y Soberano de Tamaulipas), is a state in the northeast region of Mexico; one of the 31 states which, along with Mexico City, comprise the 32 Federal Entiti ...

and

Coahuila Coahuila (), formally Coahuila de Zaragoza (), officially the Free and Sovereign State of Coahuila de Zaragoza ( es, Estado Libre y Soberano de Coahuila de Zaragoza), is one of the 32 states of Mexico. Coahuila borders the Mexican states of N ...

.Gray, Asa in Emory, William Hemsley 1859. Report on the United States and Mexican boundary survey :made under the direction of the secretary of the Interior . Botany 2(1): 87
/ref> It occurs in coastal prairie,

grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...

, and mesquite shrubland habitat. It has declined because its native habitat has been cleared for development, with remaining open

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

invaded by non-native grasses such as buffelgrass (''Cenchrus ciliaris'').USFWS
Determination of Endangered Status for the Plants ''Ayenia limitaris'' (Texas Ayenia) and ''Ambrosia cheiranthifolia'' (South Texas Ambrosia).
''Federal Register'' August 24, 1994. Today there are perhaps 20 populations remaining, but some of these may have very few genetic individuals because the species is clonal, with many cloned plants attached by one

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

.The Nature Conservancy
/ref> It is not certain that the plant still exists in Mexico.Texas Parks and Wildlife
/ref> This is a federally listed

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

of the United States. ''Ambrosia cheiranthifolia'' is a rhizomatous perennial herb growing erect to a maximum height around 40 centimeters. Several clones usually grow in a dense patch. The stems and herbage are silvery green with a coating of rough gray hairs. The oblong leaves are 3 to 7 centimeters long and oppositely arranged on the lower plant but alternate on the upper stems. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...

contains staminate

flower heads A pseudanthium (Greek for "false flower"; ) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, compos ...

in clusters with a few

pistillate Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

heads in leaf axils below the clusters.Flora of North America
/ref> This plant sometimes occurs alongside slender rush-pea (''Hoffmannseggia tenella''), another endangered species.

References

External links

{{Taxonbar, from=Q4741887 cheiranthifolia Flora of Coahuila Flora of Tamaulipas Flora of Texas Flora of the Rio Grande valleys Plants described in 1859 Taxa named by Asa Gray Endangered flora of the United States