Helianthus paradoxus

Pecos sunflower is an annual forb occurring in the southwestern United States, in widely disjunct regions in central and southern New Mexico, and in nearby Trans-Pecos, Texas. This taxon has narrow habitat requirements, only occurring in highly saline wetlands within deserts called ciénegas. These wetlands are continuously threatened by habitat degradation, groundwater withdrawal, competition from non-native species, grazing, rights-of-way maintenance, oil and gas activities, and groundwater pollution. Historically, ciénega habitat has been lost or altered as a result of development, filling, water diversion, groundwater pumping, and surface water diversion. However, critical habitat has been designated for this taxon under the Endangered Species Act, some populations have been afforded some levels of protection, and plant numbers have showed a positive response to management activities such as invasive species removal and prescribed burns.

Pecos sunflower occurs in western Texas and New Mexico in the southwestern United States (USFWS 2005, 2015, 2023). At present, it is known from two general areas in Pecos and Reeves counties of west Texas and five regions of New Mexico (USFWS 2005). The population regions are defined in the recovery plan (USFWS 2005) as follows: 1) the west-central New Mexico region, 2) the Santa Rosa region, 3) the Dexter/Rosswell region, 4) and the west Texas region. Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1984 and 2025 (RARECAT 2024, iNaturalist 2025, NatureServe 2025, SEINet 2025).

By applying a 1 km separation distance to herbarium specimen data, photo-based observation data, and NatureServe Network occurrence data documented between 1984 and 2025, there are estimated to be 25 occurrences rangewide (RARECAT 2024, iNaturalist 2025, NatureServe 2025, SEINet 2025). In New Mexico, there are an estimated 22 occurrences: two near the town of Grants, one along the Rio San Jose on the Laguna Indian Reservation, eight in or near the town of Santa Rosa, and eleven in the Pecos River Valley from just north of Roswell to just north of Dexter. The two Grants sites are near the San Jose River and separated from the Laguna population by approximately 73 km. The eight Santa Rosa sites occur within a ten square kilometer area. Ten of the eleven Pecos River sites occur within a 36 km stretch of the Pecos River Valley. In Texas, there are an estimated three occurrences: two along Diamond Y Creek north of Fort Stockton, and one at East Sandia Springs near Balmorhea. The two Diamond Y sites are within five km of each other. The Diamond Y and East Sandia Springs Preserves are within 80 km of each other. The Texas sites are approximately 241 km south of the most southerly New Mexico site.

Pecos sunflower is primarily threatened by ground water depletion and loss of wetland habitat (USFWS 1999). Additional threats include competition with non-native plants, hybridization with the common sunflower, excessive grazing by livestock, wallowing impacts by feral hogs, fire suppression, rights-of-way maintenance activities, pollution, oil and gas activities, and climate change.

Pecos sunflower occurs in springs and seeps, which are rare in arid environments. Agriculture, urban development, and the invasion of saltcedar (Tamarix sp.) have caused these wetland areas to diminish (Sivinski 1996). In Pecos and Reeves Counties, New Mexico, 48 of 61 springs are now dry, primarily due to groundwater pumping (Brune 1981). Based on county soil surveys, some sites were former marshes and possibly supported populations of Pecos sunflower. Groundwater recharge, discharge, and flow of the Roswell Artesian Basin, which supports the Roswell Oasis Dairy Cienega (critical habitat for this taxon), is considerably impacted by anthropogenic activities; including irrigation of farm fields during summer months (Cantu de Leija 2021). Populations are dependent on constant water flow and fluctuate based on water supply. A great deal of historical habitat has been lost due to falling water tables and depleted desert springs. Although the trend in wetland losses is probably slower than in the past, it is still continuing.

Pecos sunflower is threatened by the invasion of non-native plant species into spring and ciénega habitats, including invasion by saltcedar (Tamarix spp.), which forms dense thickets that shade smaller species and modifies habitats so that they become more dry and saline (USFWS 2023). One of the historical localities of Pecos sunflower in Reeves County, Texas is now almost entirely dominated by salt cedar. Pecos sunflower is also threatened by the non-native Russian olive (Elaeagnus angustifolia) that invades wetland edges. All recovery regions are currently impacted by invasives, and chemical and mechanical controls are being implemented in critical habitat regions. Management activities include prescribed fire, cut and herbicide treatment, and mechanical removal. Feral hogs are a potential threat to populations in western Texas and are known to create wallows in mud pits during the hot months of the year, potentially causing damage to plants (Texas Parks and Wildlife 2023).

Wetland habitats provide both forage and water for livestock. Unless managed correctly, livestock can significantly modify the habitat of Pecos sunflower. Some consequences of habitat modification (i.e. drying out and invasion of exotic plant species) may be more detrimental than direct grazing impacts. Studies of the effects of cattle have shown both positive and negative interactions (Van Auken and Bush 1993, 1995). Cattle eat and/or trample the plants, reducing the number of flower heads and seeds, as well as the dry mass of the stems, leaves, and flower heads. However, cattle disturbance of the surrounding vegetation may supply this species with light gaps for germination and growth, and reduce competition (Bush and Van Auken 1997). Numerous experiments have been conducted both in- and ex- situ on the effects of associated species competition on Pecos sunflower (Van Auken and Bush 1993, 1994, 1995). With competitors removed, Pecos sunflower exhibited greater basal stem diameter, produced more flower heads, and had greater flower head, leaf, and stem dry mass (Bush and Van Auken 1997).

Annual species of sunflowers hybridize in cultivation, but have reduced pollen viability and seed fertility (Heiser 1965, 1969). Under natural conditions most annual sunflower species are allopatric with the exception of the common sunflower, Helianthus annuus. Hybrids of Pecos sunflower and H. annuus have been observed at the Diamond Y Preserve in west Texas and in the Santa Rosa area of New Mexico. Pecos sunflower is a species of hybrid origin (Rieseberg et al. 1990, 1991). The parental species are H. annuus and the prairie sunflower, H. petiolaris. These two species occupy different habitats from Pecos sunflower. Helianthus annuus grows on disturbed soils that are wet in spring but dry in summer, while Helianthus petiolaris occurs on sandy, usually dry, soils. Both H. annuus and H. petiolaris bloom primarily in the spring and summer while Pecos sunflower blooms in the fall. However, H. annuus often invades disturbed sites around Pecos sunflower populations and can flower into the fall, thus opening the possibility for hybridization.

Fire suppression is a threat to Pecos sunflower, which requires open habitat. Prescribed burns can help mitigate this threat by reducing non-native plant biomass and regenerating soil nutrients. A prescribed fire at Blue Hole Cienega in 2017 significantly increased the number of plants observed along eleven monitoring transects (Roth 2021).

Although the New Mexico Highway department is working on modifying its mowing schedules, herbicide drift could still potentially affect the sunflowers' population density in the highway rights-of-way (USFWS 2005). A management and monitoring agreement between Texas Parks and Wildlife Department and the Texas Department of Transportation is in place for the one Pecos Sunflower population in Texas on highway right-of-way. Herbicides are not used in the area, and the creek has been fenced to prevent mowing.

Water contamination from oil and gas development and other source pollutants are a concern for some populations, particularly in the New Mexico Roswell/Dexter and west Texas regions (USFWS 2023). At the Diamond Y site in west Texas, there are brine pits from previous drilling activities that are potentially a source of mineral pollutants (Texas Parks and Wildlife 2023). Oil and gas pipelines occur within the spring outflow channels and marshes where Pecos sunflower occurs, and there are many active wells and pipelines located in close proximity to surface waters. In addition, an oil and gas refinery is located just 0.5 miles upstream.

Climate change and increasing aridity represents a significant threat to this wetland-dependent species, particularly as the demand for scarce water resources for agricultural and livestock uses will also likely increase during drought (USFWS 2023). Expansion of oil and gas development could also increase the demand for water resources for hydraulic fracturing.