Texas prairie dawn (Hymenoxys texana) is an extremely rare annual wildflower that is endemic to Texas Coastal Plains of Harris, Waller, Ft. Bend, Trinity and Gregg counties, and was listed as an endangered species in 1986 by the U.S. Fish and Wildlife Service. This petite, single to multi-stemmed member of the sunflower family bears 6 millimeter-tall yellow flower heads in late February to early April, as documented by E.L. Bridges in 1988. Basal leaves are spoon-shaped, with entire or toothed margins. Stem leaves are alternate, narrow with parallel sides and have no, to few, teeth on margins. Seeds are cone-shaped and mature in April and May. The plants occur in small patches dispersed among sparsely vegetated areas, known as slick spots, on slightly saline soils at the base of pimple or mima mounds or within almost barren areas in open grasslands, as documented by D.M. Young and L.E. Brown in 1989. Texas prairie dawn is adapted to these saline conditions, but is out-competed by other vegetation where soils exhibit lower salt levels, as noted in the 1989 recovery plan. Changes in hydrology of native soils due to development or over-growth of woody vegetation, especially Chinese tallow trees (Triadica sebifera), degrade the habitat necessary for Texas prairie dawn to propagate or grow, as noted in the 5-year review of 2015. Common soil series associated with Hymenoxys texana consist of primarily Gessner complex and Katy find sandy loam, as documented in the National Cooperative Soil Survey in 2012. Soils often covered with a blue-green algae. Notable plant associations may include Thurovia triflora, Choris texensis, Valerianella florifer, Willkommia texana var. texana, and Atriplex texana, along with 12 other regionally restricted species for a total of 378 associated taxa, as documented by J.R. Singurst and others in 2014.
The Texas prairie dawn is member of the sunflower family (Asteraceae, Helenieae) and is a single-stemmed or branching annual reaching a height of up to 6 inches. Basal leaves are spoon-shaped, with entire or toothed margins. Stem leaves are alternate, narrow with parallel sides and have no, to few, teeth on margins. Flowers are yellow with a cluster of flowers less than one half inch long. These plants flower in early March through April, depending on wet conditions in winter. Seeds are cone-shaped and mature April to May.
Not much is known about pollination biology, which includes the breeding system and pollinators that help Texas prairie dawn to reproduce. Successful sexual reproduction is especially important in monocarpic annuals, like Hymenoxys texana. The U.S. Fish and Wildlife Service plans to gather this information using Section 6 Funds to determine what factors are associated with successful reproduction, what obstacles limit population maintenance and establishment and define the baselines that can be used as more specific targets for this species recovery, including defining typical seed set rate and requirements for outcrossing, for example.
Texas prairie dawn is found in small, conspicuous, sparsely-vegetated areas of fine, sandy and compact soils. These bare spots are often located on the lower sloping portions of mima or pimple mounds, as noted in the 1989 recovery plan. Mima mounds are low, roughly-circular elliptical domes or shield-like mounds, often with flat tops, that are composed of unstratified sandy loam soils which are coarser than, and distinct from, the surrounding less coarse and often clayey soil. Mima mounds range from 1 to 30 meters in diameter, and attain heights from about 10 centimeters to over 2 meters, as documented by D.L. Johnson and J.L. Horwath Burnham in 2012. Common soil series associated with Texas prairie dawn consist of primarily Gessner complex and Katy find sandy loam. Texas prairie dawn flowers from early March through mid to late April. The early flowering period is a result of specific wet conditions that are available on the bare and saline slick spots where the plant is found. These spots tend to dry out to almost desert like conditions during the hot summer months. Cool and wet winters tend to produce conditions that are favorable for increased and more robust flowers. However, drought conditions, like those observed following the winters from 2009 to 2011, may impede growth of the plant resulting in fewer individuals, as noted in the 5-year review in 2015. Alternatively, excessively prolonged wet winters can reduce the number of plants present as observed after wet winter of 2015 and also following flood conditions from Hurricane Harvey in August 2017.
The land near a shore.
Land on which the natural dominant plant forms are grasses and forbs.
Environments influenced by humans in a less substantial way than cities. This can include agriculture, silvaculture, aquaculture, etc.
In 2012, W. C. Holmes and others described Hymenoxys perpygmaea as a new annual species. This species, which is ephemeral, is endemic to an alfisol prairie that contains mima mounds in Lamar County from northeastern Texas. It is similar to Hymenoxys texana, but is easily distinguished from that species by its diminutive rosette and fewer florets per capitulum.
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