Hymenoxys texana
Encyclopedia
Hymenoxys texana is a rare species of flowering plant in the aster family
known by the common names prairie dawn, Texas prairie dawn-flower, and Texas bitterweed. It is endemic to Texas
, where it is known only from the general vicinity of Houston
. It is threatened by the loss of its habitat. It is a federally listed endangered species
of the United States.
This is an annual herb with delicate reddish or purplish stems growing only 10 or 15 centimeters tall. The leaves have rubbery, glandular blades which may be simple or divided into lobes, particularly at mid-stem. The inflorescence
is a solitary flower head
or an open cluster of several heads. Each head is under a centimeter wide and has 6 to 8 tiny yellow ray florets each 2 or 3 millimeters long. The ray florets are often tucked behind the phyllaries
.
This plant grows only in the grassland
s of the Gulf Coastal Plain
in Texas. It can be found on open, barren stretches of saline sandy soil at the base of Mima mounds
. The soil is often coated with a slick of algae (Nostoc
sp.) during the wet season. The soil dries, cracks, and becomes powdery in the dry season. Few other plants occur on this substrate, but prairie dogshade (Limnosciadium pumilum) can sometimes be associated.
This plant is known only from Harris
and Fort Bend Counties
in Texas. It was first described in 1891 from a specimen taken near Hockley
. Few specimens were noted after this and by 1979 the species was thought to be extinct
. Just two years later it was relocated. Today there are about 50 populations, but most all of these are endangered by the destruction and degradation of their habitat. Most of the occurrences of the plant are within or near the Houston metropolitan area
, which is undergoing rapid growth. Habitat is being claimed for residential and other development.
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
known by the common names prairie dawn, Texas prairie dawn-flower, and Texas bitterweed. It is endemic to Texas
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...
, where it is known only from the general vicinity of Houston
Houston, Texas
Houston is the fourth-largest city in the United States, and the largest city in the state of Texas. According to the 2010 U.S. Census, the city had a population of 2.1 million people within an area of . Houston is the seat of Harris County and the economic center of , which is the ...
. It is threatened by the loss 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 is an annual herb with delicate reddish or purplish stems growing only 10 or 15 centimeters tall. The leaves have rubbery, glandular blades which may be simple or divided into lobes, particularly at mid-stem. 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 solitary flower head
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
or an open cluster of several heads. Each head is under a centimeter wide and has 6 to 8 tiny yellow ray florets each 2 or 3 millimeters long. The ray florets are often tucked behind the 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...
.
This plant grows only in the 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...
s of the Gulf Coastal Plain
Western Gulf coastal grasslands
The Western Gulf coastal grasslands are a subtropical grassland ecoregion of the southern United States and northeastern Mexico. It is known in Texas as "Coastal Prairie" and as the Tamaulipan pastizal in Mexico.-Setting:...
in Texas. It can be found on open, barren stretches of saline sandy soil at the base of Mima mounds
Mima Mounds
Mima mounds is a term used for low, flattened, circular to oval, domelike, natural mounds found in the northwestern United States, Idaho, Oregon, and Washington, that are composed of loose, unstratified, often gravelly sediment that is an overthickened A Horizon...
. The soil is often coated with a slick of algae (Nostoc
Nostoc
Nostoc is a genus of cyanobacteria found in a variety of environmental niches that forms colonies composed of filaments of moniliform cells in a gelatinous sheath.The name "Nostoc" was invented by Paracelsus...
sp.) during the wet season. The soil dries, cracks, and becomes powdery in the dry season. Few other plants occur on this substrate, but prairie dogshade (Limnosciadium pumilum) can sometimes be associated.
This plant is known only from Harris
Harris County, Texas
As of the 2010 Census, the population of the county was 4,092,459, White Americans made up 56.6% of Harris County's population; non-Hispanic whites represented 33.0% of the population. Black Americans made up 18.9% of the population. Native Americans made up 0.7% of Harris County's population...
and Fort Bend Counties
Fort Bend County, Texas
Fort Bend County is a county located along the Gulf Coast region in the U.S. state of Texas within the Houston–Sugar Land–Baytown metropolitan area. In 2000 its population was 354,452, while the 2010 U.S...
in Texas. It was first described in 1891 from a specimen taken near Hockley
Hockley, Texas
Hockley, Texas is an unincorporated community located in Harris County, Texas, United States along on Texas State Highway 6, approximately five miles southeast of the city hall of Waller, and thirty-six miles northwest of Downtown Houston....
. Few specimens were noted after this and by 1979 the species was thought to be extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
. Just two years later it was relocated. Today there are about 50 populations, but most all of these are endangered by the destruction and degradation of their habitat. Most of the occurrences of the plant are within or near the Houston metropolitan area
Greater Houston
Houston–Sugar Land–Baytown is a 10-county metropolitan area defined by the Office of Management and Budget. It is located along the Gulf Coast region in the U.S. state of Texas...
, which is undergoing rapid growth. Habitat is being claimed for residential and other development.