SOUTH TEXAS AMBROSIA

South Texas ambrosia of the Asteraceae family is typically found in clay-loam to sandy-loam prairies and savannas. It is an herbaceous, silvery to grayish green plant that grows erect and blooms in the fall with non-showy flowers. It grows from rhizomes, which result it in existing as a clonal population of plants with simple leaves that are opposite on the lower part of the plant and alternate at the top portion. Its staminate flowers are arranged in terminal racemes, while its pistillate flowers are arranged in small clusters located in the leaf axils below the staminate racemes.

TAXONOMY

DISTRIBUTION

HISTORY

REFERENCES

TAXONOMY

Ambrosia cheiranthifolia

DISTRIBUTION

South Texas ambrosia grows and blooms at low elevations in open clay-loam prairies and savannas among Ayenia limitaris, Buchloe dactyloides, Stipa leucotricha and Bouteloua rigidiseta. South Texas ambrosia was first collected in San Fernando, Tamaulipas, Mexico, by Luis Berlandier in 1835. The first U.S. collection was made by Robert Runyon in 1932 in Cameron County, Texas. It has since been found in Cameron, Wells, Kleberg and Nueces in South Texas. Six populations are known to exist: two in Nueces County, one in Kleberg discovered in 1992 by Ruth O'Brien and three in Nueces County discovered in 1992 and 1993 by William Carr.

HISTORY

In 1975, a report on endangered, threatened or extinct plants was first presented to Congress by the Smithsonian Institution. In 1976, South Texas ambrosia was included among seventeen-hundred plants considered endangered in a published report, but in 1978, the proposal was withdrawn due to new amendments to the Endangered Species Act, which stated that any proposals over two years old be withdrawn. In 1983, a status report on South Texas ambrosia was finally completed with sufficient information to deem the species as endangered.

One of the main factors involved in South Texas ambrosia becoming endangered is habitat destruction. Its native brush and woodlands have continuously been converted to agricultural fields, improved pastures or urban areas. These areas have also been cleared for urban water development, industrial development and flood control. Remaining species along roads have also suffered from blading, plowing and seeding with other more exotic plants. Another factor affecting South Texas ambrosia is lowered genetic variability. Its populations are clonal and their reduced numbers have caused them to be more vulnerable to the ill-effects of lowered genetic diversity.

The fact that South Texas ambrosia suffers from a limited distribution, low population numbers and threats of habitat destruction results in its being considered an endangered plant species.

REFERENCES

U.S. Fish and Wildlife Service - Division of Endangered Species

Texas Parks and Wildlife page

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