field thistle

(Cirsium discolor)

               
Conservation Status

IUCN Red List

not yet assessed

field thistle

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

Nativity

Native

 
Occurrence

Common

 
Habitat

Dry to moderate moisture. Prairies, fields, forest openings, river bottoms, roadsides, disturbed areas. Full sun.

 
Flowering

July to October

     
Flower Color

Pale pinkish-purple

     
Height

36 to 84

     

Identification

This is a 36 to 84 tall, erect, biennial or short-lived perennial forb that rises on a single stem from a slightly thickened taproot and fibrous roots.

The stems are erect with few to many ascending branches. They are covered with long, white, spreading, unmatted, soft hairs when young, becoming almost hairless as they age. They are not winged and do not have spines.

In the first year the plant appears as a rosette of basal leaves. In the second year it sends up a flowering stem.

Basal leaves are firm, broadly lance-shaped to egg-shaped or elliptic in outline, 4 to 20 long, and 1½ to 9 wide, but usually no more than 10 long and 5 wide. They are bluntly angled or sometimes rounded at the tip and taper at the base to a winged leaf stalk. They are deeply lobed (pinnatifid), the lobes cut more than halfway to the midrib. The upper surface is green and hairless or moderately covered with stiff, straight hairs. The lower surface is white and densely covered with felty hairs. The margins are coarsely toothed, spiny, and rolled under. Basal leaves are usually absent at flowering time.

Stem leaves are similar, alternate, stalkless, 1½ to 10 long, and to 5 wide, becoming smaller as they ascend the stem. The leaf bases are sometimes somewhat clasping but do not extend down along the stem. The leaves at the branch tips are smaller. The upper leaves are well developed.

The inflorescence is usually a single flower head, sometimes a few flower heads, at each branch tip. The flower heads are stalkless or on short stalks (peduncles). The peduncles are leafy, up to 2 long, and are not overtopped by upper stem leaves. Each head is subtended by a ring of spiny, leaf-like bracts. These bracts arch upward and encage the developing flower head at first, spreading gradually as the head matures.

The whorl of bracts at the base of the flower head (involucre) is egg-shaped to broadly cylinder- or bell-shaped, ¾ to 1 long, and to 13 16 wide, as long or longer than wide. It usually has a few cobwebby hairs. The bracts of the involucre have a 1 16 to 3 16 long, straw-colored spine at the tip.

The flower heads are 1½ to 2 wide. There are numerous pale, pinkish-purple, tubular flowers.

The fruit is a tan to brownish, to 3 16 long achene (cypsela). The cypsela has a straw-colored collar near the tip and a tuft of white hairs at the tip.

 
Similar
Species

Bull thistle (Cirsium vulgare) stems have wings with spiny margins. The leaf bases extend down along the stem. The underside of the leaf is green.

Flodman’s thistle (Cirsium flodmanii) is a shorter plant, usually no more than 32 in height. The stems remain densely white tomentose with age. The upper leaf surface is tomentose when young. The flower head is not subtended by a ring of spiny bracts. The flower head is smaller, no more than 1 wide. The collar on the cypsela is yellow and conspicuous.

Tall thistle (Cirsium altissimum) leaves are shallowly lobed, the lobes cut less than of the way to the midrib.


Distribution Distribution Map   Sources: 2, 3, 4, 5, 7, 22, 28.

Comments

 


Taxonomy

Family:

Asteraceae (aster)

 

Subfamily:

Carduoideae

 

Tribe:

Cynareae

 

Subtribe:

Carduinae

 
Synonyms

Carduus discolor

 
Common
Names

field thistle

pasture thistle


 

 

 

 

 

 

 

 

 

 

Glossary

achene

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 entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.

 

bract

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

 

involucre

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

 

peduncle

The stalk of a single flower or flower cluster.

 

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.

 

tomentose

Densely covered with short, soft, matted or tangled, woolly, usually white or silvery hairs.

 

wing

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

       

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Flower Head

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  Cirsium discolor (Pasture Thistle)
Allen Chartier
 
  Cirsium discolor (Pasture Thistle)  
     
  Cirsium discolor PASTURE THISTLE
Frank Mayfield
 
  Cirsium discolor PASTURE THISTLE  

 

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  Georgia State Undergraduate Reseach Conference - Thistle
Georgia State University
 
   
 
About

Published on Apr 8, 2014

These undergrads are among nearly 150 students whose work will be highlighted at the Georgia State Undergraduate Research Conference on Thursday, April 10 at the University Center. Students will share their findings through oral presentations, posters, artistic displays, and performances. The event is free and open to the public.

RANDI ALLEN, AMALIA GRAELL AND ADANI PUJADA

Year: Seniors

Major: Biology, College of Arts and Sciences

Title of Research Project: "Antimicrobial Activity of Cirsium discolor Flower Extract against Staphylococcus aureus and Acinetobacter baummannii"

The Project:
When it comes to fighting bacterial infections, modern medicine is starting to lose the war. Bacteria are becoming increasingly resistant to every antibiotic that's in a doctor's arsenal, and scientists are working to find new ways to fight infections as the old medicines fail.

Allen, Graell and Pujada looked to see if Cirsium discolor, a type of field thistle, could fight two different bacteria. One, Staphylococcus aureus is the source of staph infections that can cause numerous diseases: pneumonia, heart failure and severe bone inflammation. Acinetobacter baummannii is a stubborn organism that often makes its home in hospitals, causing infections that are incredibly difficult to treat with existing antibiotics.

While this particular thistle is known to help lower blood pressure, scientists have never investigated whether it could fight bacteria -- until now. Through their research, this undergraduate team found that there is a chemical compound in the thistle's extract that fights both species of bacteria.

Choosing the Research Subject:
For Pujada, the possibility of new discoveries in medicine in nature was exciting. She, Allen and Graell took a class on medicinal plants, taught by their research faculty sponsor, Maria Nagy.

"I liked the idea of picking out our own plants, then going back to use those plants to help find new antibiotics," she said.

Fun Fact:
When not busy in the lab, Allen likes to try her hand in the kitchen.

"I enjoy Cake Boss and shows like that, and I play and mimic like I'm on the show," she said. "I have my family members try out the disasters -- and sometimes they taste good, sometimes not so much."

 
     

 

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