stiff sunflower

(Helianthus pauciflorus ssp. subrhomboideus)

               
Conservation Status

IUCN Red List

not yet assessed

stiff sunflower (ssp. subrhomboideus)

NatureServe

NNR - Unranked

SNR - Unranked

Minnesota

not listed

Nativity

Native

Occurrence

Common

Habitat

Dry to moderately wet. Prairies, upland forest openings, pastures, railroads, roadsides.

Flowering

July to September

     
Flower Color

Yellow ray florets, reddish-brown to purple disk florets

     
Height

12 to 48

     

Identification

This is an erect, 12 to 48 tall, annual forb that rises on a single stem from long, thick, branched, creeping rhizomes. It often forms colonies.

The stems are erect, green or reddish-brown, and unbranched or sparingly branched near the top. They are rough to the touch due to a moderate to dense covering of short, stiff, ascending to spreading hairs. The stems are usually leafless near the top.

There are usually 5 to 10 leaf nodes below the inflorescence. Lower leaves are opposite, uppermost leaves are usually also opposite. Lower and middle leaves are rhombic egg-shaped to lance-linear, relatively thick, and flat, not folded longitudinally. They are 2 to 4¾ long and ¾ to 2 wide, 2½ to 8 times as long as wide. They are wedge-shaped at the base and taper to a blunt or sharp point at the tip with straight sides along the tip. The upper and lower surfaces are rough to the touch due to a moderate to dense covering of minute, stiff hairs. They are also sparsely to moderately covered with minute, stalkless, yellow glands. The margins are finely toothed to almost untoothed. The leaves have 3 main veins, a midvein and a pair of lateral veins that branch off the main vein well above the base and arch upward.

The inflorescence is sometimes a solitary head, usually an open cluster of 2 to 10 flower heads at the end of the stem. The flower heads are on stalks that are 13 16 to 4¾ long.

The whorl of bracts at the base of the flower head (involucre) is to in diameter. The bracts of the involucre are elliptic to egg-shaped and taper to a blunt or sharp point at the tip. The tips of the bracts are tightly appressed.

The flower heads are 1½ to 2½ wide, the disk is to 1 in diameter. There are 10 to 20 yellow ray florets and 75 or more reddish-brown to purple disk florets.

The fruit is an achene.

 
Similar
Species

Stiff sunflower (Helianthus pauciflorus ssp. pauciflorus) tends to be taller, 32 to 60 in height. There are usually 5 to 15 leaf nodes below the inflorescence. The uppermost leaves are usually alternate. The lower and middle leaves are longer, 3 to 10 long. They are oblong lance-shaped to narrowly egg-shaped and taper to a sharp point at the tip with concave sides along the tip.


Distribution Distribution Map   Sources: 3, 4, 7, 28.

Comments

What’s in a Name?
The species name pauciflorus means few-flowered.

Allelopathy
The roots exude chemicals that inhibit seed germination and growth of young plants. When in a dense colony, these chemicals may cause the inner plants to die, leaving a ring of living plants.


Taxonomy

Family:

Asteraceae (aster)

 

Subfamily:

Asteroideae

 

Supertribe:

Helianthodae

 

Tribe:

Heliantheae (sunflower)

 
Parent

stiff sunflower (Helianthus pauciflorus)

 
Synonyms

Helianthus laetiflorus var. subrhomboideus

Helianthus pauciflorus var. subrhomboideus

Helianthus rigidus ssp. laetiflorus

Helianthus rigidus var. subrhomboideus

Helianthus rigidus ssp. subrhomboideus

Helianthus subrhomboideus

 
Common
Names

few-leaved sunflower

prairie sunflower

stiff sunflower


 

 

 

 

 

 

 

 

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.

 

Allelopathy

The release of a chemical toxin by one plant to inhibit the growth or germination of nearby competing plants.

 

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.

 

Linear

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

 

Node

The small swelling of the stem from which one or more leaves, branches, or buds originate.

 

Rhizome

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

       

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  stiff sunflower (ssp. subrhomboideus)   stiff sunflower (ssp. subrhomboideus)
       

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  stiff sunflower (ssp. subrhomboideus)    
       
       

 

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