N.& P. Holmgren
Identity
Unique IDELEMENT_GLOBAL.2.146639
Element CodePDASC02290
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single nation
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderGentianales
FamilyApocynaceae
GenusAsclepias
Other Common NamesWelsh's milkweed (EN)
Concept ReferenceKartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2024-05-03
Change Date2024-05-03
Edition Date2024-05-03
Edition AuthorsRoth, E., rev. D. Atwood, rev. B. Franklin (1996), rev. D. Roth/K. Gravuer (2006), rev. S Schuetze (2012), rev. N. Ventrella (2024)
Threat ImpactVery high - high
Range Extent5000-20,000 square km (about 2000-8000 square miles)
Number of Occurrences6 - 20
Rank ReasonsAsclepias welshii is an herbaceous perennial with deep taproots and horizontally-spreading rhizomes that is found in active dune habitat in Utah (Kane County), Arizona (Coconino County), and Navajo Nation tribal lands in the western United States. This species is known from nine population areas with an estimated total of 74,000 stems (ramets), although the number of genetic individuals (genets) that this represents is unknown. Overall ramet numbers increased since the last population census from approximately 16,000 stems to 74,000 stems, with the majority of stems found at the Coral Pink Sand Dunes population in Utah. Stem declines were recorded at six out of the nine populations, however, and four out of nine populations now have less than 104 stems. The two Utah occurrences face the greatest threats, with parts of the species' very fragile sand dune habitat impacted primarily by off-road vehicle (OHV) activity. The four Navajo Nation occurrences are smaller but are relatively remote. The two occupied areas on BLM land in Arizona are also remote and not affected by OHV disturbance. Climate change and drought also pose a likely (though currently unknown) threat to this species.
Range Extent CommentsAsclepias welshii occurs in North America, in south-central Utah (Kane County), northern Arizona (Coconino County), and in northern Arizona on Navajo Nation tribal lands of the United States (USFWS 2015).
Occurrences CommentsThere are nine known populations of Asclepias welshii; two occurring in southern Utah (Kane County), four occurring in northern Arizona (Coconino County), and an additional three occurring on Navajo Nation tribal lands near Tuba City and Kayenta (Coconino County) (USFWS 2021).
Threat Impact CommentsThe most significant threats identified to Asclepias welshii that contributed to its listing as threatened under the U.S. Endangered Species Act (ESA) in 1987 were off-road vehicle (OHV) use and inadequacies of regulatory mechanisms protecting the species (USFWS 1987). The Coral Pink Sand Dunes (CPSD) population, which contains approximately 97% of the known stems of this species, is heavily used by off-road vehicles for recreation (USFWS 2015), although 27% of designated critical habitat within CPSD is closed to OHV use. Off-road vehicle use is also prohibited for populations occurring in the Paria Canyon-Vermilion Cliffs Wilderness area in northern Arizona and at the Sand Hills population in Utah. There are no restrictions to OHV use for populations occurring on the Navajo Nation, but significant OHV use was not observed (NatureServe 2024), likely due to the remoteness of those populations. Off-road vehicle use has a direct negative impact to plants by crushing or uprooting ramets, but also may have a positive impact by destabilizing dune habitats and discouraging vegetation growth (Robinson 2019). A more robust evaluation of the impacts of OHV use to this species within CPSD is needed (USFWS 2021). An additional threat to this species is climate change, though very little is known about the species' response to climate factors. Livestock grazing and insect predation were also noted as impacting individuals, but these threats were considered to have little to no impact to the species as a whole (USFWS 2015).