Regularity: Regularly occurring
Global Range: Coastal south Texas (Cameron, Kleberg, Jim Wells, Nueces Cos.) south to Tamaulipas, Mexico.
Ambrosia cheiranthifolia may be characterized by median leaves of flowering stems entire and silky-pubescent (Correll and Johnston, 1970).
Comments: Grasslands and various mesquite-dominated shrublands on soils ranging from heavy clays to lighter-textured sandy loams. Most commonly found in coastal prairie communities over the Quaternary-age Beaumont Formation.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 6 - 20
Comments: About 15-20 occurrences: 5 in S. Texas (Cameron, Kleberg, Jim Wells, Nueces Cos.) and 1 in Tamaulipas, Mexico.
Life History and Behavior
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G2 - Imperiled
Reasons: Only an estimated 20 population centers survive, and since most popluations are clonal, these may represent very few genetically different individual plants. The species' geographic range is limited to coastal south Texas and northeastern Mexico. Much of its original habitat has been converted to agricultural fields and pastures. The remnant, fragmented native prairies and savannahs are threatened by continued habitat distruction, agricultural chemicals, and by invasive, non-native grasses, which are commonly planted in the area.
Date Listed: 08/24/1994
Lead Region: Southwest Region (Region 2)
Listing status: E
For most current information and documents related to the conservation status and management of Ambrosia cheiranthifolia, see its USFWS Species Profile
Comments: Threatened by continued habitat distruction, agricultural chemicals, and by invasive, non-native grasses, which are commonly planted in the area.
Biological Research Needs: Population biology; habitat requirements.
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 and the Mexican state of Tamaulipas, where it occurs in coastal prairie, grassland, and mesquite shrubland habitat. It has declined because its native habitat has been cleared for development, with remaining open savanna invaded by non-native grasses such as buffelgrass (Cenchrus ciliaris). 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. It is not certain that the plant still exists in Mexico. This is a federally listed endangered species of the United States.
This 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 contains staminate flower heads in clusters with a few pistillate heads in leaf axils below the clusters.
Names and Taxonomy
Comments: Distinct species in large genus.
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