|Listed||July 19, 1984|
|Description||Perennial herb with gray, linear, woolly leaves and yellow flowers.|
|Habitat||Open scrub and brush community in sandy loam.|
|Threats||Poor reproduction, restricted range.|
Ashy dogweed, Thymophylla tephroleuca, is a perennial herb with stiff, erect stems up to 12 in (30 cm) in height. Leaves are linear and covered with soft, woolly, ashy-white hairs. When crushed, leaves emit a pungent odor. Flowers are pale to bright yellow and about 1 in (2.5 cm) in diameter. In poorer habitats, plants are shorter, have fewer and smaller flowers, and a less dense covering of hairs. The plant blooms from March to May, depending on rainfall. The gray cast of the leaves makes this plant very conspicuous from a distance. This species has also been referred to as Dyssodia tephroleuca.
The ashy dogweed grows in fine, sandy-loam soil in clearings within a scrub and brush community. Precipitation averages about 20 in (51 cm) per year, and prolonged drought is common. Dominant plants in the habitat are mesquite, yucca, buffelgrass, goatbush, ceniza, anacahuita, and javelina brush. Habitat elevation is between 400-415 ft (122-126 m).
Ashy dogweed was known historically from two populations in extreme southwestern Texas, bordering the Rio Grande River. A population in Starr County was extirpated, leaving a single surviving population in Zapata County.
In 1987 about 1,300 individual plants of this species were surveyed along a state highway right-of-way and on privately owned ranch land in Zapata County. The population occupies about 22 acres (10 hectares).
The reasons for the decline of ashy dogweed are not well understood, but poor reproductive capability is suspected because seedlings are generally absent throughout the range. Natural plant succession, changing micro-climate, competition with the non-native buffelgrass, and the disappearance of pollinators may all be factors in the poor reproduction. Many unknown aspects of this species' biology need to be studied before the decline can be reversed.
The habitat of ashy dogweed is presently used to graze livestock. Although the cattle probably do not eat the ashy dogweed, soil compaction as a result of trampling prevents seedling establishment.
A management technique in this range is to clear brush and reseed, which gives an edge to the highly competitive bufflegrass. Bufflegrass forms dense stands that shades out the lower growing ashy dogweed.
A large population of ashy dogweed occurs on a highway right-of-way, which is maintained by blade cutting and herbicides. It is believed that many individuals were killed as a result of herbicide application around the habitat, which is a continuing threat. A pipeline was also constructed through the habitat, and many plants were killed by heavy construction equipment.
Because the population is so small and the habitat conditions deteriorating, the ashy dogweed is highly susceptible to stochastic extinction and an absence of any regeneration.
Conservation and Recovery
After the Texas Natural Heritage Program identified the remaining ashy dogweed site as one of 20 state sites most in need of immediate protection, the Texas Nature Conservancy contacted local landowners to inform them of the significance of the plants on their property. Landowners appear to have responded favorably, and the next step is to negotiate conservation agreements with these landowners.
Fish and Wildlife Service personnel have consulted with the state of Texas to allow oversight of maintenance activities along the highway right-of-way. In September 1984, the staff of the San Antonio Botanical Gardens visited the ashy dogweed population to take cuttings and seeds to establish a cultivated population. This effort is being conducted with the assistance of the Center for Plant Conservation.
Correll, D. S., and M. C. Johnston. 1970. Manual of the Vascular Plants of Texas. Texas Research Foundation, Renner, Texas.
Turner, B. L. 1980. "Status Report: Dyssodia tephroleuca Blake." U.S. Fish and Wildlife Service, Albuquerque, NM.
U.S. Fish and Wildlife Service. 1986. "Recovery Plan for the Ashy Dogweed." Albuquerque, NM.