Thymophylla tephroleuca
Encyclopedia
Thymophylla tephroleuca (formerly Dyssodia tephroleuca) is a rare species of flowering plant known by the common names ashy dogweed and ashy pricklyleaf. It is endemic to Texas
in the United States, where it occurs in two counties near the Mexican border. It became rare due to the destruction and degradation of its habitat. It is a federally listed endangered species
of the United States.
This plant, a shrub
or subshrub, produces a clump of stems up to 30 centimeters tall. The herbage is ashy gray-green, gray, or whitish due to a layer of white woolly hairs. The leaves are linear to threadlike and are arranged alternately along the stems. They measure 1 to 1.5 centimeters long. The inflorescence
is a flower head
with a bell-shaped involucre of woolly-haired phyllaries
. There are 12 or 13 yellow ray florets and about 30 disc florets at the center. The fruit is an achene
with a pappus
of scales. Blooming occurs mostly in March through May but it may bloom at other times depending on rainfall.
This plant is likely a relict
, a rare species remaining in a grassland
habitat type that was once more common. Most of the local territory has converted to brushland dominated by cenizo
(Leucophyllum frutescens) blackbrush
(Coleogyne ramosissima), and creosote bush (Larrea tridentata). Other dominant plant species include mesquite (Prosopis glandulosa), goatbush (Castela texana), anacahuita (Cordia boissieri), and javelina brush (Microrhamnus ericoides). The introduced
buffelgrass (Cenchrus ciliaris) is common.
By 1979 this plant was known from a 1 acre (0.00404686 km²) in Zapata County, Texas. By the time the plant was placed on the Endangered Species List in 1984 there was a single population containing about 1300 plants. This population is bisected by a highway. More populations have been found in the years since and currently there are six in Zapata and Webb Counties
.
Threats to the species have included highway maintenance, because the plant grows directly next to a highway. Dying plants have been observed at the highway's edge, a possible sign of herbicide
application. The installation of a gas pipeline likely destroyed some plants and its maintenance is a threat to others in the area. Grazing
is not a direct threat because cattle do not eat the foul-smelling plant, but their trampling may compact the soil. The introduction of buffelgrass for better grazing has led to drastic changes in the plant community, because it spreads and competes easily with other species.
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
in the United States, where it occurs in two counties near the Mexican border. It became rare due to the destruction and degradation of its habitat. It is a federally listed endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of the United States.
This plant, a shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
or subshrub, produces a clump of stems up to 30 centimeters tall. The herbage is ashy gray-green, gray, or whitish due to a layer of white woolly hairs. The leaves are linear to threadlike and are arranged alternately along the stems. They measure 1 to 1.5 centimeters long. The inflorescence
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. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
is a flower head
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
with a bell-shaped involucre of woolly-haired phyllaries
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
. There are 12 or 13 yellow ray florets and about 30 disc florets at the center. The fruit is an achene
Achene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
with a pappus
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
of scales. Blooming occurs mostly in March through May but it may bloom at other times depending on rainfall.
This plant is likely a relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
, a rare species remaining in a grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
habitat type that was once more common. Most of the local territory has converted to brushland dominated by cenizo
Leucophyllum frutescens
Leucophyllum frutescens is an evergreen shrub in the figwort family, Scrophulariaceae, native to the state of Texas in the southwestern United States and the states of Coahuila, Nuevo León, and Tamaulipas in northern Mexico. Although commonly known as Texas Sage, it is not a true sage and is...
(Leucophyllum frutescens) blackbrush
Coleogyne
Coleogyne is a monotypic genus in the rose family containing the single species Coleogyne ramosissima, which is known by the common name blackbrush. This thorny, aromatic shrub is native to the deserts of the southwestern United States. It is a thickly branched thicket which may spread across the...
(Coleogyne ramosissima), and creosote bush (Larrea tridentata). Other dominant plant species include mesquite (Prosopis glandulosa), goatbush (Castela texana), anacahuita (Cordia boissieri), and javelina brush (Microrhamnus ericoides). The introduced
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
buffelgrass (Cenchrus ciliaris) is common.
By 1979 this plant was known from a 1 acre (0.00404686 km²) in Zapata County, Texas. By the time the plant was placed on the Endangered Species List in 1984 there was a single population containing about 1300 plants. This population is bisected by a highway. More populations have been found in the years since and currently there are six in Zapata and Webb Counties
Webb County, Texas
Webb County is a county located in the U.S. state of Texas. The official 2010 population for the county is 250,304. In 2000, its population was 193,117, and in 2006 its population had been estimated to have reached to 231,470. Its county seat is Laredo...
.
Threats to the species have included highway maintenance, because the plant grows directly next to a highway. Dying plants have been observed at the highway's edge, a possible sign of herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
application. The installation of a gas pipeline likely destroyed some plants and its maintenance is a threat to others in the area. Grazing
Grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
is not a direct threat because cattle do not eat the foul-smelling plant, but their trampling may compact the soil. The introduction of buffelgrass for better grazing has led to drastic changes in the plant community, because it spreads and competes easily with other species.