Identity
Unique IDELEMENT_GLOBAL.2.1203075
Element CodePDASC022L0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderGentianales
FamilyApocynaceae
GenusAsclepias
SynonymsAsclepias uncialis ssp. uncialis
Concept ReferenceRiser II, J.P., S.L. Emel, and E.H. Roalson. 2019. Genetics and ecological niche define species boundaries in the dwarf milkweed clade (Asclepias: Asclepiadoideae: Apocynaceae). International Journal of Plant Science 180(2):160-177.
Taxonomic CommentsWhile historically the taxonomy of the dwarf milkweeds has fluctuated between one and four species, Riser et al. (2019) did comprehensive molecular, genetic, ecological studies and habitat modeling that has led to greater clarity of the taxonomy of this group. Riser et al. (2019) determined that there are in fact 4 distinct species in this group: Asclepias uncialis, A. eastwoodiana, A. sanjuanensis and A. ruthiae. These taxa are geographically separated which aids in their identification at the state level. Asclepias uncialis occurs Colorado, south to New Mexico, and into the far southeastern portion of Arizona. There are also populations known in the panhandles of Oklahoma and Texas.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2021-06-09
Change Date2021-06-09
Edition Date2021-06-09
Edition AuthorsSpackman, Susan (1995), rev. D. Gries (1998), rev. K. Decker (2007), rev. Treher (2021)
Threat ImpactVery high - high
Range Extent200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Number of Occurrences21 - 80
Rank ReasonsAsclepias uncialis is a milkweed that occurs in the southwestern United States and adjacent Mexico. It is found in Arizona, Colorado, New Mexico, Oklahoma, and Texas. There are less than 60 occurrences that occur sporadically in desert grasslands or shortgrass prairies across the species range. The largest population size documented is around 150 plants. This species has experienced historical declines due to the conversion of lands for agriculture and residential development. More recent declines in habitat quality and population sizes are due to incompatible land uses, like heavy grazing, invasive species, and off road vehicle use. Surveys are needed to identify new populations in potential habitat and to document that status of threats, trends, and abundance of plants rangewide.
Range Extent CommentsAsclepias uncialis occurs in the United States from western Great Plains of eastern Colorado, south through New Mexico, and into the far southeastern portion of Arizona. There are also populations known in the panhandles of Oklahoma (Cimarron County) and Texas (Andrews and El Paso Counties) (Riser et al. 2019). There is a report from a grassland site in the Animas Valley of Sonora, Mexico, just south of the species range in the United States (SEINet 2021). Range extent was calculated using NatureServe Network data as of 2021 and herbarium records (SEINet 2021).
Occurrences CommentsAs currently understood, there are less than 60 occurrences of this species despite significantly more suitable habitat (Riser er al. 2019).
Threat Impact CommentsThe species habitat, shortgrass prairie, is generally threatened by extensive human alterations for agricultural, residential, and recreational uses. Specific threats to extant occurrences include recreational use (off road vehicles and hikers), grazing by cattle, invasive species including Bromus tectorum, and military tank traffic.