poke milkweed

(Asclepias exaltata)

Conservation Status
poke milkweed
  IUCN Red List

LC - Least Concern

     
  NatureServe

N5 - Secure

SNR - Unranked

     
  Minnesota

not listed

     
           
Wetland Indicator Status
     
  Great Plains

FAC - Facultative

     
  Midwest

UPL - Obligate upland

     
  Northcentral & Northeast

UPL - Obligate upland

     
           
 
Description
 
 

Poke milkweed is an erect perennial forb. A single stem rises from a large rhizome. The leaves and stems contain a milky juice.

The stems are erect, light green, and hairless.

The leaves are opposite, thin, elongated, 4 to 8 long, up to 3 wide, and broadly elliptical. They taper to a point both at the tip and at the base. They are attached to the stem on to ¾ leaf stalks. The upper surface is hairless. The margins are untoothed and may be slightly wavy.

The inflorescence is few to several loose, few-flowered, umbrella-shaped clusters (umbels) rising from the upper leaf axils.

The structure of the typical milkweed flower is unique and instantly recognizable. There are 5 petals bent backward at the base and hanging downward. Subtending the petals are 5 much shorter, light green, lance-shaped sepals. There are 5 stamens. Formed from the filament of each stamen is a petal-like appendage. The appendage consists of a tubular hood surrounding an awl-shaped horn in the center of the hood. The stamens and the stigma are fused together into a crown-like structure (gynostegium). Each stigma has a long slit designed to catch the legs of a pollinating insect. A small, dark, sticky gland above this slit is attached to pollen sacs from adjacent anthers. These glands are designed to break off as an insect pulls its leg free of the slit, and remain attached to the insects leg. The flowers are pollinated by larger insects strong enough to lift off with the pollen sacs attached. Smaller insects are caught in a death trap or leave behind their detached legs.

The flowers of this plant are shaped like the typical milkweed flower. They droop at the end of long, slender flower stalks. They are about ½ tall and wide. The petals are green or green tinged with purple. They bend backward at the base, hang downward, then curl upward near the tip. They are separated from the hoods by a short but distinct column. The hoods are white or purplish-white. The horns are much longer than the hoods. They project from the hoods and are curved inwards.

The fruit is an elongated, pointed, spindle-shaped, 4¾ to 6 long pod. It is held erect or ascending on a downward-curved stalk. It opens on one side exposing the seeds to spreading by the wind. The seeds have a tuft of silky hairs at the tip.

 
     
 

Height

 
 

3 to 5

 
     
 

Flower Color

 
 

Green or greenish-white petals, white or purplish-white hoods

 
     
 

Similar Species

 
 

The thin leaves pointed at both ends, loose few-flowered umbels, and white or purplish-white flowers drooping at the end of long flower stalks distinguish this from other milkweeds in Minnesota.

 
     
 
Habitat
 
 

Moist. Upland woods.

 
     
 
Biology
 
 

Flowering

 
 

June to July

 
     
 
Use
 
 

Faunal Associations

 
 

Milkweeds are the only plants that Monarchs lay their eggs on. The eggs are laid on the underside of healthy young leaves.

 
     
 

Toxicity

 
 

This and other milkweeds contain cardiac glycosides and may be poisonous to both humans and livestock.

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 5, 7, 28.

 
  3/29/2018      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

 

 
         
 
Taxonomy
 
  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (dicots)  
  Superorder Asteranae  
 

Order

Gentianales (gentians, dogbanes, madders, and allies)  
 

Family

Apocynaceae (dogbane)  
  Subfamily Asclepiadoideae (milkweed)  
  Tribe Asclepiadeae  
  Subtribe Asclepiadinae  
 

Genus

Asclepias (milkweed)  
       
 

Subordinate Taxa

 
 

 

 
       
 

Synonyms

 
 

Asclepias bicknellii

Asclepias phytolaccoides

Asclepias polystachya

Asclepias syriaca var. exaltata

 
       
 

Common Names

 
 

poke milkweed

tall milkweed

 
       

 

 

 

 

 

 

 

 

Glossary

Axil

The upper angle where the leaf stalk meets the stem.

 

Clasping

Describing a leaf that wholly or partly surrounds the stem but does not fuse at the base.

 

Glaucous

Pale green or bluish gray due to a whitish, powdery or waxy film, as on a plum or a grape.

 

Gynostegium

A crown-like structure of plants of the genus Asclepias formed by the fusion of the anthers with the stigmas.

 

Linear

Long, straight, and narrow, with more or less parallel sides, like a blade of grass.

 

Rhizome

A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.

 

Umbel

A flat-topped or convex, umbrella-shaped cluster of flowers or buds arising from more or less a single point.

       
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Plant

  poke milkweed   poke milkweed
       
  poke milkweed   poke milkweed
       

Inflorescence

  poke milkweed   poke milkweed
       

Flower

  poke milkweed    
       

Leaves

  poke milkweed   poke milkweed
       
  poke milkweed   poke milkweed
       
       

 

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