swamp thistle

(Cirsium muticum)

Conservation Status
swamp thistle
  IUCN Red List

not listed

     
  NatureServe

N5 - Secure

SNR - Unranked

     
  Minnesota

not listed

     
           
Wetland Indicator Status
     
  Great Plains

FACW - Facultative wetland

     
  Midwest

OBL - Obligate wetland

     
  Northcentral & Northeast

OBL - Obligate wetland

     
           
 
Description
 
 

Swamp thistle is a 12 to 90 tall, erect, biennial forb that rises from fibrous roots and a cluster of fleshy, stout, white to brown roots, rarely from a single taproot. The first year it appears as a rosette of basal leaves. The second year it sends up a single flowering stem.

Basal leaves are egg-shaped to broadly elliptic or inversely egg-shaped in outline. They can be 6 to 21½ long, and 1½ to 8 wide, though they are usually no more than 12 long and 4 wide. They are on spiny-winged leaf stalks. The leaf blade is tapered at the base and deeply lobed (pinnatifid), the lobes cut of the way to the midrib. The lobes are linear to lance-shaped and are sometimes lobed again. They taper to a point at the tip with straight or concave sides along the tip. The upper surface is green and nearly hairless or sparsely covered with short, curled hairs. The lower surface is green and nearly hairless or sparsely covered with long, soft, cobwebby hairs. The margins have a few irregular teeth and many fine, soft spines, the main ones 1 16 to long. Basal leaves are usually absent at flowering time.

The stem is erect, light green, ridged, and round in cross section. It has a few to many ascending branches, mostly above the middle. It may be hairless or sparsely covered with long, soft, spreading hairs, especially near the base. It is not winged and is not covered with a whitish, waxy substance (glaucous).

Stem leaves are alternate and 1¼ to 6 long. The leaf blade is pinnatifid, the lobes relatively narrow and cut more than ½ of the way to the midrib. It is otherwise similar to basal leaves. Lower stem leaves are stalked. Stem leaves become smaller and shorter stalked but no less divided as they ascend from the middle of the stem toward the inflorescence. Upper stem leaves are stalkless, well developed, and often slightly clasp the stem at the base.

The inflorescence is a single flower head or a more or less open, branched, cluster (corymb) of 2 to 5 flower heads at the end of each branch. The flower heads are stalkless or are borne singly on up to 6 long stalks (peduncles). At the base of each peduncle there is a single 1 to 3 long, leaf-like bract. The corymbs are sometimes overtopped by the uppermost leaves. The flower heads are not subtended by a ring of spiny, leaf-like bracts.

The whorl of bracts at the base of the flower head (involucre) is broadly cylinder-shaped or bell-shaped, to 1¼ long, and to 1¼ wide. It is often somewhat cobwebby hairy. The bracts of the involucre (phyllaries) are in 8 to 12 series. They are green with a dark green central (dorsal) patch surrounding a white, gummy, sticky ridge. The outer (lower) and middle phyllaries are egg-shaped and taper to a appressed or ascending, sharply or bluntly pointed tip. The inner phyllaries are linear. The phyllaries are tipped with minute, insignificant spines. They appear spineless except under close examination.

The flower heads are to 1¼ to 2 in diameter and have numerous tubular disk flowers. The disk flowers are to 1¼ long and reddish-purple or dark purple, rarely white

The fruit is a dark brown, to 3 16 long seed capsule (cypsela). The cypsela has a conspicuous yellow collar near the tip and a tuft of white or slightly grayish-tinged hairs at the tip.

 
     
 

Height

 
 

12 to 90

 
     
 

Flower Color

 
 

Purple to pink

 
     
 

Similar Species

 
 

 

 
     
 

The Native Thistle Test

 
 

Thistles native to Minnesota do not have spiny stems. Grasp the stem near the base of any native thistle loosely in your fist, then slide your fist upwards to just below the inflorescence. If the plant is a native thistle, you will not get a single prickle – it will be “ouchless”. If the thistle is thought to be an exotic (non-native) species, this test is not recommended. Tall thistle is native.

 
     
 
Habitat
 
 

Wet. Meadows, prairies, marshes, swamps, bogs, woodland openings, streambanks. Full sun.

 
     
 
Biology
 
 

Flowering

 
 

July to October

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

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

 
  6/28/2017      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

Common

 
         
 
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 (flowering plants)  
  Superorder Asteranae  
 

Order

Asterales (sunflowers, bellflowers, fanflowers, and allies)  
 

Family

Asteraceae (sunflowers, daisies, asters, and allies)  
  Subfamily Carduoideae (thistles and allies)  
  Tribe Cynareae (= Cardueae)  
  Subtribe Carduinae (thistles and burdocks)  
  Genus Cirsium (thistle)  
       
 

Cardueae is a synonym of the tribe name. Cynareae was published first and has precedence. Nevertheless, most sources use the name Cardueae for the tribe.

 
       
 

Subordinate Taxa

 
 

 

 
       
 

Synonyms

 
 

Carduus muticus

Cirsium bigelovii

Cirsium muticum var. monticola

Cirsium muticum var. subpinnatifidum

 
       
 

Common Names

 
 

dunce-nettle

horsetops

swamp thistle

thistle

 
       

 

 

 

 

 

 

 

 

Glossary

Bract

Modified leaf at the base of a flower stalk, flower cluster, or inflorescence.

 

Corymb

A flat-topped or convex inflorescence in which the stalked flowers grow upward from various points on the main stem to approximately the same horizontal plane. The outer flowers open first.

 

Cypsela

A dry, one-chambered, single-seeded fruit, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed from the wall of the inferior ovary and also from other tissues derived from the receptacle or hypanthium, does not split open at maturity, but relies on decay or predation to release the contents.

 

Glaucous

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

 

Involucre

A whorl of bracts beneath or surrounding a flower or flower cluster.

 

Linear

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

 

Peduncle

In angiosperms, the stalk of a single flower or a flower cluster; in club mosses, the stalk of a strobilus or a group of strobili.

 

Phyllary

An individual bract within the involucre of a plant in the Asteraceae family.

 

Pinnatifid

Deeply cut, more than half way to the midrib but not to the midrib, into lobes that are spaced out along the midrib; the lobes do not form separate leaflets.

 

Wing

A thin, flat, membranous, usually transparent appendage on the margin of a structure.

       
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Plant

  swamp thistle   swamp thistle
       

Inflorescence

  swamp thistle    
       

Corolla

  swamp thistle   swamp thistle
       

Involucre

  swamp thistle   swamp thistle
       
  swamp thistle    
       

Leaves

  swamp thistle   swamp thistle
       
       

 

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