sawtooth sunflower

(Helianthus grosseserratus)

               
Conservation Status

IUCN Red List

not yet assessed

sawtooth sunflower

NatureServe

N5? - Secure

SNR - Unranked

Minnesota

not listed

Wetland
Indicator
Status

Great Plains

FACW - Facultative wetland

Midwest

FACW - Facultative wetland

Northcentral & Northeast

FACW - Facultative wetland

Nativity

Native

 
Occurrence

Common

 
Habitat

Dry. Prairies, bluff tops, railroads, roadsides, and open, disturbed areas. Full sun. Sandy soil.

 
Flowering

June to September

     
Flower Color

Yellow ray florets, reddish-brown to purple disk florets

     
Height

24 to 120

     

Identification

This is an erect perennial forb that rises on a single stem from a short creeping rhizome or sometimes a longer, thick, branched rhizome. It often forms dense colonies. It can be up to 120 tall when appearing as a single plant, 24 to 60 tall when in a colony.

The stems are erect, stout, round, and green, becoming purple in strong sun. They are sometimes covered with a whitish, waxy bloom (glaucous). They are hairless and usually unbranched below the inflorescence. Within the inflorescence the stems are sparsely to moderately covered with short, appressed, upward pointing hairs.

There are usually 20 to 25 stem leaves. There are no basal leaves. Lower and middle stem leaves are usually alternate, sometimes opposite. Those near the top are always alternate. Lower stem leaves are narrowly lance-shaped to narrowly egg-shaped, 4 to 12½ long and 1½ to 3½ wide, 5 to 10 times as long as wide. They are often folded along the midrib, especially during hot and dry weather. They are on ¾ to 2 long leaf stalks. They are wedge-shaped at the base and taper to a sharp point at the tip. The upper surface is dark green and smooth or slightly rough and sparsely to moderately covered with minute hairs. The lower surface is densely covered with minute, soft, appressed hairs. The margins are coarsely or shallowly toothed. The leaves have a prominent midvein, and a pair of lateral veins that branch off the main vein well above the base and arch upward. The first pair of lateral veins is only slightly more prominent than subsequent pairs.

The inflorescence is occasionally a solitary head, usually an open, branched cluster of 3 to 15 or more flower heads at the end of the stem.

The flower heads are 2½ to 4 wide with disk up to wide. They are on stout stalks that are up to 4 long. There is a whorl of 25 to 30 bracts (involucre) in 2 or 3 overlapping series at the base of the flower head. The involucre is broadly hemispheric in shape and to 1 in diameter. The bracts are loosely spreading or sometimes ascending, and are spreading or bent backward at the tip. They are narrowly lance-shaped to nearly linear, and taper to a sharply-pointed tip. They are hairless or hairy toward the base, and have a fringe of hairs along the margin, at least near the base.

There are 14 to 20 yellow ray florets and 100 or more yellow disk florets.

The fruit is an achene.

 
Similar
Species

See the Sunflowers ID Filter for a spreadsheet (Microsoft Excel 2007) to aid identification of this and similar species.

Rydberg’s sunflower (Helianthus nuttallii ssp. rydbergii) leaves are on shorter stalks, 3 16 to long. The leaf blades are smaller, 1½ to 8 long and 5 16 to 1½ wide. The margins are untoothed or sparingly toothed. The inflorescence has fewer flower heads, no more than 6. The involucre has 30 to 38 bracts. The flower head has fewer disk florets, 60 or more. In Minnesota it is rare, currently verified in only one location.


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

Comments

 


Taxonomy

Family:

Asteraceae (aster)

 

Subfamily:

Asteroideae

 

Supertribe:

Helianthodae

 

Tribe:

Heliantheae (sunflower)

 
Synonyms

Helianthus grosseserratus var. hypoleucus

Helianthus grosseserratus ssp. maximus

Helianthus instabilis

 
Common
Names

saw-tooth sunflower

sawtooth sunflower

thick-tooth 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 or flower cluster.

 

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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  Helianthus grosseserratus SAWTOOTH SUNFLOWER
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  Helianthus grosseserratus SAWTOOTH SUNFLOWER  

 

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