Rydberg’s sunflower

(Helianthus nuttallii ssp. rydbergii)

Conservation Status
Rydberg’s sunflower
  IUCN Red List

LC - Least Concern

     
  NatureServe

N3N5 -Vulderable to Secure

S3 - Vulnerable

     
  Minnesota

Special Concern

     
           
Wetland Indicator Status
     
  Great Plains

FACW - Facultative wetland

     
  Midwest

FACW - Facultative wetland

     
  Northcentral & Northeast

FACW - Facultative wetland

     
           
 
Description
 
 

Rydberg’s sunflower is an erect perennial forb that rises on one or a few stems from a short, branched rhizome. It can be from 40 to 100 tall, though in Minnesota it is usually no more than 80 in height.

The stems are erect, usually yellowish-brown or green, and sometimes covered with a whitish, waxy bloom (glaucous). They are sometimes branched near the top. Below the inflorescence they are usually hairless though they sometimes are sparsely covered with short, stiff hairs.

There are no basal leaves. Lower and middle stem leaves are opposite, those near the top are alternate. They are on 3 16 to long leaf stalks. The leaf blades are lance-shaped to nearly egg-shaped and flat, not folded longitudinally. They are 1½ to 8 long and 5 16 to 1½ wide. They are wedge-shaped at the base and taper to a point at the tip with straight sides along the tip. The upper surface is green and rough to the touch due to the presence if short, stiff hairs. The lower surface is covered with short or minute stiff hairs. The margins are untoothed or sparingly, shallowly toothed. The leaves have 3 main veins, a midvein and a pair of lateral veins that branch off the main vein above the base and arch upward.

The inflorescence is a solitary head or an open, branched cluster of 2 to 6 flower heads at the end of the stem. The flower heads are on stout, to 7 long stalks.

The whorl of 30 to 38 bracts at the base of the flower head (involucre) is hemispheric in shape and to ¾ in diameter. The bracts of the involucre are loose, spreading, almost hairless, lance-shaped to lance egg-shaped, and taper to a sharply-pointed tip.

The flower heads are 3 to 3½ wide with a to ¾ wide disk. There are 10 to 21 yellow ray florets and 60 or more yellow disk florets.

The fruit is an achene.

 
     
 

Height

 
 

40 to 80

 
     
 

Flower Color

 
 

Yellow ray florets, yellow disk florets

 
     
 

Similar Species

 
 

Sawtooth sunflower (Helianthus grosseserratus) leaves are on longer stalks, ¾ to 2 long. The leaf blades are larger, 4 to 12½ long, and 1½ to 3½ wide. The margins are always toothed. The inflorescence has up to 15 flower heads. The involucre has 25 to 30 bracts. The flower head has 100 or more disk florets.

 
     
 
Habitat
 
 

Moist to moderately moist. Prairies, wetland margins. Full sun.

 
     
 
Biology
 
 

Flowering

 
 

Early August to mid-September

 
     
 

Pests and Diseases

 
 

Sunflower bullet gall midge (Pilodiplosis helianthibulla) makes ¼ in diameter, almost globe-shaped galls on the leaves of plants in the genus Helianthus.

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

3, 4, 5, 7, 28, 30.

The map at the left shows historical records in light green. The only known current population in Minnesota, aside from the one sighting listed below, is in Foxhome Prairie, in Wilkin County, shown in dark green. There may also be a population in Buffalo River State Park, where it was recorded in 1962. It is likely that other populations exist in other western counties.

 
  3/19/2021    
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

Rare

 
         
 
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 Asteroideae  
  Supertribe Helianthodae  
  Tribe Heliantheae (sunflowers and allies)  
  Subtribe Helianthinae  
  Genus Helianthus (sunflower)  
  Species Helianthus nuttallii (Nuttall’s sunflower)  
       
 

Subordinate Taxa

 
 

 

 
       
 

Synonyms

 
 

Helianthus nuttallii var. rydbergii

Helianthus rydbergii

 
       
 

Common Names

 
 

Nuttall’s sunflower

Rydberg’s 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.

 

Bract

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

 

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.

 

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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Plant

  Rydberg’s sunflower   Rydberg’s sunflower
       
  Rydberg’s sunflower    
       

Flower Head

  Rydberg’s sunflower   Rydberg’s sunflower
       
       

 

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