Asclepias hirtella    (Pennell) Woods.

Prairie Milkweed 


MN Status:
threatened
Federal Status:
none
CITES:
none
USFS:
none

Group:
vascular plant
Class:
Dicotyledoneae
Order:
Gentianales
Family:
Asclepiadaceae
Life Form:
forb
Longevity:
perennial
Leaf Duration:
deciduous
Water Regime:
terrestrial
Soils:
loam
Light:
full sun
Habitats:

(Mouse over a habitat for definition)


Best time to see:

  Foliage   Flower   Fruit  
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Asclepias hirtella Asclepias hirtella

Click to enlarge


Map Interpretation

Map Interpretation

  Synonyms

Acerates hirtella

  Basis for Listing

Asclepias hirtella appears to be rare or declining in several of the states along the northern periphery of its range, as well as in Canada and some of the eastern states. There is no indication of a serious decline in the center of its range. It may, however, be vulnerable to a decline because native habitats in that region are intensively exploited for agricultural purposes.

Woodson first reported the presence of A. hirtella in Minnesota in 1954, but he did not cite a specimen or give a location. Initial surveys of state and regional herbaria by the Minnesota DNR failed to locate a supporting specimen. Consequently, the status of this species in Minnesota remained unresolved until 1979 when a wildlife manager discovered a population at the Cartney Wildlife Management Area in Mower County. Several other sight reports have been traced to confusion with A. viridiflora (green milkweed), a similar species. Asclepias hirtella, which was listed as a threatened species in Minnesota in 1984, is quite rare in Minnesota and may be declining. This is indicated by the recent loss of major tracts of prairie habitat in southern Minnesota. Most of these tracts were not adequately inventoried for plants, but they may have sustained populations of this species before they were destroyed.

  Description

The genus Asclepias has highly specialized flowers that produce five-hooded bodies that frequently bear incurved horns or crests. In A. hirtella, the hoods are present but the horns are absent. Flowers are greenish with a distinct purplish tinge and appear in lateral umbels borne on slender stalks. Leaves are alternate, linear, very numerous, and crowded. Stems are stout and covered with short, soft, downy hairs. Asclepias hirtella bears a superficial resemblance to A. viridiflora but can be distinguished from it by the relatively long, slender stalks of the lateral flower clusters.

  Habitat

The population at Cartney Wildlife Management Area occurs in an unbroken mesic prairie. It was acquired by the DNR in the 1960s and managed for wildlife habitat. Management included a prescribed burn in 1978, soon after which A. hirtella was first noticed.

  Biology / Life History

Asclepias hirtella has a large array of pollinators, including bees, wasps, butterflies, moths, and beetles. Each smooth seedpod has numerous seeds that have a tuft of white to tan hairs that facilitate wind dispersal. It is a long-lived perennial and reproduces only by seed.

The best time to search for A. hirtella is when it is flowering, from June through July.

  Conservation / Management

The only known population of A. hirtella in Minnesota occurs on publicly owned land, so its habitat is probably safe from conversion to commercial or residential uses. Actual threats to its habitat have not been fully assessed but could include encroachment by woody species, either native or non-native, and invasion by non-native herbaceous species such as Euphorbia esula (leafy spurge) or Bromus inermis (smooth brome). Herbicides could also be a threat, either as drift from nearby agricultural fields or from the wildlife management area itself. Prescribed burns may be a useful management tool to help control encroaching brush, but the timing of a burn is critical. It should be in early spring when A. hirtella is still dormant. Once the plant has appeared above ground, a fire could do serious damage.

  Conservation Efforts in Minnesota

No conservation efforts specific to this species have been undertaken to date.

  References

Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.

Voss, E. G. 1996. Michigan Flora. Part III: Dicots (Pyrolaceae-Compositae). Cranbrook Institute of Science Bulletin 61 and University of Michigan Herbarium, Ann Arbor, Michigan. 622 pp.