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Plant Profile

Greene's Milkweed (Asclepias uncialis ssp. uncialis)

Asclepias uncialis ssp. uncialis Photo Credit: Alex Seglias

Global Rank: G2 - Imperiled
Legal Status: N/A
Family: Apocynaceae
State: AZ, CO, NM, OK, UT
Nature Serve ID: 1203075
Lifeform: Forb/herb
Date Inducted in National Collection:

Description:

A small, herbaceous perennial with several to many stems 1 to 2.5 inches high. Stems have milky sap. Leaves are primarily opposite, and are of two different forms - lower leaves are oval to lanced shaped, while upper leaves are much narrower. Flowers have five reflexed petals with attendant hoods and horns. Flowers of A. uncialis ssp. uncialis are rose-purple, appearing in clusters at the tips of the stems, and are reported to have a strong fragrance (Zimmerman 1993).

Where is Greene's Milkweed (Asclepias uncialis ssp. uncialis) located in the wild?

Habitat:

Typical habitat for Asclepias uncialis ssp. uncialis is level to gently sloping terrain without notable micro-topographic features. Although plants are often found at the base of escarpments or mesas, the species does not occur on rock ledges or outcroppings, and is absent from highly disturbed habitats such as sand dunes, erosion channels, wash slopes, and badlands. Elevations of extant occurrences in Colorado range from 3,920-7,640 feet (1,190-2,330 m). Soils in the range of A. uncialis ssp. uncialis belong to orders characterized by dry, warm soils (Mollisols, Entisols, Aridisols, and Alfisols). Asclepias uncialis ssp. uncialis does not appear to have highly specific microsite requirements, and there is no evidence that A. uncialis ssp. uncialis is restricted to a particular soil type. Occurrences are known from soils derived from a variety of substrates, including sandstone, limestone, and shale, but are most often found in sandy loam soils. It does not occur in pure sand. Asclepias uncialis ssp. uncialis is primarily associated with species typical of shortgrass prairie. Associated vegetation is comprised mostly of grasses, with forbs, shrubs, and trees typically comprising less than 15% of the total vegetation cover. Plants are typically found growing in open spaces between bunch grasses. Associated forbs are variable throughout the range, since many species found with A. uncialis ssp. uncialis in southeastern Colorado (e.g., Melampodium leucanthum) are near the northern edge of their distribution in that area (Locklear 1996). Although A. uncialis ssp. uncialis is often associated with Juniper Woodland and Savanna ecological systems, it is always found in the prairie or grassland components of these systems.

Distribution:

Historically, this species appears to have been known from two or three disjunct geographical areas: the western Great Plains of eastern Colorado, northeastern New Mexico, and the adjacent Oklahoma.

States & Provinces:

Greene's Milkweed can be found in Arizona, Colorado, New Mexico, Oklahoma, Utah

Which CPC Partners conserve Greene's Milkweed (Asclepias uncialis ssp. uncialis)?

Denver Botanic Gardens

Not Sponsored

Conservation Actions

Assigned 06/09/17

CPC's Plant Sponsorship Program provides long term stewardship of rare plants in our National Collection. We are so grateful for all our donors who have made the Plant Sponsorship Program so successful. We are in the process of acknowledging all our wonderful plant sponsorship donors on our website. This is a work in progress and will be updated regularly.

Conservation Actions

08/19/2020

Seed collection and storage.

08/19/2020

Seed collection and storage.

Nature Serve Biotics

05/02/2017

Asclepias uncialis ssp. uncialis ( = A. uncialis sensu stricto) is apparently very rare with tiny population sizes. This species and its habitat are in decline.

Greene, Mary VB Goshorn

01/01/2010

In general, A. uncialis habitat, shortgrass prairie, is threatened by extensive human alterations for agricultural, residential, and recreational uses. Specific threats to extant occurrences include: recreational use, agricultural use, and military tank t

Greene, Mary VB Goshorn

01/01/2010

6 - 20 occurrences. Most of the occurrences documented from Colorado, New Mexico, Arizona, and Wyoming are historical and general records. All of the known extant occurrences are restricted to 6 sites: Garden Park (CO), Sheep Pen Canyon Road (CO), Pueblo Reservoir (CO), Van Bremer Arroyo (CO), Sonoita (AZ) and Shiprock (NM). It is likely that further survey will locate additional occurrences. Jim Locklear (Kansas Arboretum) recognizes a total of 18 extant occurrences range wide as of May 1997.

Greene, Mary VB Goshorn

01/01/2010

On both BLM and USFS Sensitive Species lists

Greene, Mary VB Goshorn

01/01/2010

Occurrences of Asclepias uncialis are small and generally isolated from each other. The species also has extremely low rates of sexual reproduction. These factors, and the fact that A. uncialis is apparently absent from many locations where it was collected historically make it difficult to confirm that populations are stable. There is some indication that A. uncialis requires intact native habitat; however, before appropriate conservation elements can be identified, surveys and research to define the distribution, abundance, and population ecology of the species are needed. A more accurate picture of population numbers, occurrence extent, and variability will allow the identification of conservation targets. Additional investigation of the biology and ecology of A. uncialis will eventually allow land managers to formulate management strategies for the conservation of the species (Decker 2006).

Greene, Mary VB Goshorn

01/01/2010

Seed collection and storage.