Texas Ayenia

Ayenia limitaris

Description

Texas ayenia is a pubescent subshrub approximately 2-5 ft (0.6-1.5 m) tall, with alternate, simple leaves. The cordate-based leaves are approximately 3 in (7.5 cm) long and 1.4 in (3.5 cm) wide. The inflorescences are axillary, up to four per node, with each inflorescence supporting two or more perfect flowers. Flower color has been reported as green, pink, or cream. The fruit is a five-celled, pubescent capsule approximately 0.3 in (0.8 cm) long, with short, curved prickles.

Habitat

Texas ayenia occurs at low elevations in dense subtropical woodland communities. Previous collectors have found the plant in openings within chaparral and along the edges of thickets. The present site is a Texas Ebony-Anacua (Pithecellobium ebano-Ehretia anacua ) plant community located within the Arroyo Colorado drainage. This area was once an active flood plain; however, the effect of past flooding on Texas ayenia is unknown.

The Texas Ebony-Anacua plant community, which occurs on well drained, but heavy soils on riparian terraces, once covered much of the Rio Grande delta. Canopy cover is close to 95% in this climax community type. Associated species include la coma (Bumelia celastrina ), brasil (Condalia hookeri ), granjeno (Celtis pallida ), and snake-eyes (Phaulothamnus spinescens ). The Texas Ebony-Anacua community grades into the Texas Ebony-Snake-eyes community in the drier portions of the woodland habitat. Both plant communities have been reduced to discontinuous fragments, often surrounded by agricultural fields, pastures, or urban development, and now cover less than five percent of their original area.

Distribution

Texas ayenia occurred historically in Cameron and Hidalgo Counties in the United States, and the states of Coahuila, Nuevo Leon, and Tamaulipas in Mexico.

The only recent collection in Mexico was from a Tamaulipan population in 1981; however, the present status of this population is unknown. Texas ayenia has not been relocated at any of the historic Cameron County locations since the early 1960s. A status report noted a 1988 observation of six spindly plants at the Hidalgo County site, and the following year only one individual was observed.

Searches were undertaken in 1990 and 1991 by a number of personnel from the U.S. Fish and Wildlife Service and Texas Parks and Wildlife Department, but no plants were found. In 1992, Service personnel and Jim Everitt of the U.S. Department of Agriculture located one plant at the Hidalgo County site. In 1994, Joe Ideker located 20 additional plants at this site. This site, on private property, is the only one recently verified for the species.

Threats

Habitat destruction is the primary threat to Texas ayenia. The past and current practices of converting native South Texas brush and woodlands to agricultural fields, improved pastures, and urban areas, or clearing brush and woodlands for urban water development, industrial development, or flood control, have destroyed 95 percent of this native vegetation. Most native Texas Gulf Coast prairies have been converted to agricultural fields or improved pastures. The amount of conversion of these plant communities in Mexico is similar though not quantified. The remaining remnant, native prairie, brush, and woodland tracts are often surrounded by agricultural fields, pastures, or urban development. These modified habitats pose potential threats to the native areas through agricultural chemical drift from aerial spraying; chemical runoff following rains; invasion of non-native grasses such as buffelgrass, guinea grass (Panicum maximum ), King Ranch bluestem, and Angleton bluestem (Dichanthium aristatum ); and trampling and possible collection pressures due to easy accessibility from nearby urban areas. The few remaining populations of the species are vulnerable to extinction if any of their remaining habitat is modified.

Even roadside remnants of native vegetation in South Texas are often bladed, or plowed and seeded with exotic grasses such as buffelgrass and King Ranch bluestem. Herbicides are often used to control vegetation around signs, guard rails, and bridge abutments, and to kill shrubby vegetation encroaching on the right-of-way. Due to the rarity of Texas ayenia and South Texas ambrosia, the likelihood they will be directly impacted by roadway maintenance is small, but almost any impact could lead to extinction of either species.

With only one known verified population, Texas ayenia may have low genetic variability, which could limit its ability to adapt to environmental changes. It is unknown whether past flooding created or maintained habitat for Texas ayenia. However, since the present population occurs within a previously active drainage of the Arroyo Colorado, a flood could negatively impact the species. Observers have noted that the population declined during the recent drought in the Lower Rio Grande Valley. The extreme rarity of this species makes it vulnerable to extinction from any number of chance events.

Conservation and Recovery

Some federal actions that may affect Texas ayenia include brush clearing for flood control by the International Boundary and Water Commission, management recommendations to landowners by the Soil Conservation Service for activities funded by the Agricultural Stabilization and Conservation Service, and agricultural pesticide registration by the Environmental Protection Agency. Additionally, a population of South Texas ambrosia occurs on Kingsville Naval Air Station and may be affected by maintenance or construction activities at this facility. These agencies have been notified of the occurrence of the endangered plants so that appropriate conservation steps may be taken.

Contact

Corpus Christi Ecological Services Field Office
U.S. Fish and Wildlife Service
Texas A & M University at Corpus Christi
P.O. Box 9136
Corpus Christi, Texas 78469

Reference

U. S. Fish and Wildlife Service. 24 August 1994. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Plants Ayenia limitaris (Texas Ayenia) and Ambrosia cheiranthifolia (South Texas Ambrosia)." Federal Register 59 (163): 43648-43652.