whorled milkweed

(Asclepias verticillata)

Conservation Status
whorled milkweed
 
  IUCN Red List

not listed

     
  NatureServe

N5 - Secure

SNR - Unranked

     
  Minnesota

not listed

     
           
Wetland Indicator Status
     
  Great Plains

FACU - Facultative upland

     
  Midwest

FACU - Facultative upland

     
  Northcentral & Northeast

UPL - Obligate upland

     
           
 
Description
 
 

Whorled milkweed is a 8 to 20 tall, erect, perennial herb that rises from a rhizome and fleshy roots. It often forms colonies. The leaves and stems contain a milky juice.

The stems are erect, unbranched below the inflorescence, and ridged. They have short, soft hairs in lines on the ridges.

The leaves are numerous in whorls of 3 to 6. They are linear and are attached to the stem without a leaf stalk. They may be erect, semi-erect, or spreading. The blades are ¾ to 3 long, less than wide, with pointed tips. The margins are untoothed and rolled backward toward the underside.

The inflorescence is several loose, small, umbrella-shaped clusters (umbels) rising from the upper leaf axils. The clusters are 2 to 3 in diameter and are on a ½ to 1½ long stalk. They typically have 10 to 20 flowers.

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 are about ¼ tall, wide, and are attached on ¼ to ½ long thread-like stalks. The petals are greenish white and are tinged with purple near the tip. They bend backward at the base, hang downward, then curl upward near the tip. They are separated from the hoods by a distinct column. The hoods are white. The horns are white and are longer than the hoods. They project from the hoods and bend inwards. There is little or no fragrance.

The fruit is a narrow, spindle-shaped pod. It is 3 to 4 long and ¼ to wide. It is held erect or ascending on an erect stalk. It opens on one side exposing the seeds to spreading by the wind. The seeds have a tuft of hairs at the tip that are whitish and about 1 long.

 
     
 

Height

 
 

8 to 20

 
     
 

Flower Color

 
 

White horns, greenish-white petals tinged with purple

 
     
 

Similar Species

 
 

Prairie milkweed (Asclepias hirtella) is a much taller plant, 16 to 40 tall at maturity. The leaves are longer and narrower, lance-shaped to linear, and alternate. It has 2 to 10 flower clusters. The clusters have 30 to 100 flowers.

Green milkweed (Asclepias viridiflora) leaves are much wider, lance-shaped to oblong, mostly opposite, with wavy margins. It usually has just 1 to 3 flower clusters. The clusters have 20 to 80 flowers. The flowers are not tinged with purple. The petals are attached directly to the hoods, not separated by a column.

 
     
 
Habitat
 
 

Dry. Prairies, fields, open upland woods, roadsides.

 
     
 
Biology
 
 

Flowering

 
 

July to September

 
     
 

Pests and Diseases

 
 

 

 
     
 
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, 24, 28, 30.

 
  10/21/2021      
         
 

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 parviflora

 
       
 

Common Names

 
 

eastern whorled milkweed

horsetail milkweed

whorled milkweed

 

 

 

 

 

 

 

 

 

 

 

Glossary

Axil

The upper angle where the leaf stalk meets the stem.

 

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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Nancy Falkum

 
 

Whorled Milkweed

 
    whorled milkweed      
           
 
MinnesotaSeasons.com Photos
 
 

Plant

 
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Inflorescence

 
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    whorled milkweed      
           
 

Flowers

 
    whorled milkweed      
           
 

Leaves

 
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Infructescence

 
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Camera

     
 
Slideshows
 
  Asclepias verticillata WHORLED MILKWEED
Frank Mayfield
 
  Asclepias verticillata WHORLED MILKWEED  
  A. verticillata
Joshua Mayer
 
  A. verticillata  
 
About

Whorled Milkweed

 

 

slideshow

       
 
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Other Videos
 
  Honeybee forages on whorled milkweed
Robert Klips
 
   
 
About

Uploaded on Jul 10, 2011

A Honeybee forages on whorled milkweed, Asclepias verticillata, on July 8, 2011 at Killdeer Plains Wildlife Area in Wyandot County, Ohio, USA.

   

 

Camcorder

 
 
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  Nancy Falkum
7/22/2021

Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit

whorled milkweed  
           
 
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