great St. Johnswort

(Hypericum ascyron ssp. pyramidatum)

Conservation Status
great St. Johnswort
  IUCN Red List

not listed

     
  NatureServe

NNR - Unranked

SNR - Unranked

     
  Minnesota

not listed

     
           
Wetland Indicator Status
     
  Midwest

FAC - Facultative

     
  Northcentral & Northeast

FAC - Facultative

     
           
 
Description
 
 

Great St. Johnswort is a showy, mid-summer wildflower. It occurs in the northeastern United States from Maine to Minnesota, south to New Jersey and Missouri, and in southern Ontario and Quebec Canada. Within this range it is common, but for an unknown reason large populations are seldom found. It is speculated that the wide distribution of small populations is due to dispersal by Native Americans, who may have eaten its fruits. In Minnesota it is common in the eastern half of the state and mostly absent from the western half. It is found in moist areas, including in woodland openings, moist meadows and thickets, river-bottom prairies, ravines in upland prairies, and fens; on the banks of rivers and streams; and in roadside ditches. It grows under full sun to light shade in a variety of soil conditions. It blooms in Minnesota in July and August.

Great St. Johnswort is an erect, perennial forb, rising on a single stem or more often on 2 or more stems from a somewhat woody base. The base sometimes develops short, horizontal, underground stems (rhizomes). The plant can be 20 to 78 (50 to 200 cm) tall but is usually no more than 52 (130 cm) in height.

The stems are hairless; erect or curve up at the base (ascending); unbranched on the lower two-thirds and often branched near the top; and green, sometimes tinged with red. The upper part of the stem is four-angled and slightly ridged or narrowly winged below each leaf. On older plants the surface of the upper stem often peels in thin strips.

The leaves are opposite, stalkless, 1916 to 3 (40 to 85 mm) long, and 1116 to 1716 (18 to 37 mm) wide. The leaf blade is mostly narrowly oval and widest at the middle (elliptic) or below the middle (ovate), sometimes lance-shaped. It is shallowly heart-shaped at the base, often somewhat surrounding (clasping) the stem, and tapers to a bluntly pointed or rounded tip. There is a single main vein, visible on the lower half of the blade, and 4 to 7 pairs of lateral veins. The smallest (tertiary) veins form a dense network. There are no black dots, lines, or streaks, but there are usually pale to yellowish-brown dots visible. The upper surface is medium green, hairless, and sometimes has a whitish, waxy coating (glaucous). The lower surface is pale green and hairless. The margins are flat and untoothed.

The inflorescence is a single flower or a flat-topped to rounded cluster (cyme) of 2 to 5 flowers at the end of the stem and each branch. A single plant can have up to 35 flowers.

Each flower is 1316 to 2¾ (30 to 80 mm) in diameter and is on a stalk (pedicel) that is no more than ½ (13 mm) long, rather short relative to the size of the flower. The pedicel lengthens in fruit, becoming up to 1316 (30 mm) long. There are 5 sepals, 5 petals, about 120 to 160 stamens, and 5 styles. The sepals are green, oblong lance-shaped to narrowly egg-shaped, 516 to ½ (8 to 13 mm) long, and 316 to ¼ (5 to 6 mm) wide. They do not have noticeable yellowish-brown or black dots, lines, or streaks. The petals are bright yellow, widely spreading, narrowly to broadly oval and widest near the tip (obovate), 1 to 1916 (25 to 40 mm) long, and about ¾ (20 mm) wide. They often develop white streaks as they age. The stamens are fused near the base of their stalks (filaments) into 5 groups of about 30 each. The filaments and anthers are yellow. The pistil is light green. The styles are united for most of their length, separated just at the tip. The stigmas are cap-like.

The fruit is an egg-shaped, to 1316 (9 to 30 mm) long, 316 to ½ (5 to 13 mm) wide capsule with 5 cells and numerous seeds. The capsule is egg-shaped, widest near the base and tapered to a short beak. The seeds are oblong, flattened, and black when mature.

 
     
 

Height

 
 

20 to 78 (50 to 200 cm)

 
     
 

Flower Color

 
 

Bright yellow

 
     
 

Similar Species

 
     
     
 
Habitat
 
 

Moist. Woodland openings, moist meadows and thickets, river-bottom prairies, ravines in upland prairies, fens, the banks of rivers and streams, and roadside ditches. Full sun to light shade.

 
     
 
Biology
 
 

Flowering

 
 

July and August

The flowers are pollinated mostly by bumblebees.

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 5, 7, 24, 28, 29, 30.

 
  9/15/2021      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

Common in eastern Minnesota

 
         
 
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 (dicots)  
  Subclass Rosidae  
  Superorder Rosanae  
 

Order

Malpighiales (nances, willows, and allies)  
 

Family

Hyperiaceae (St. Johnswort)  
  Tribe Hypericeae  
  Genus Hypericum (St. Johnswort)  
  Section Roscyna  
  Species Hypericum ascyron  
       
 

There are three subspecies of Hypericum ascyron. Two are native to Asia and do not occur in North America. Only one, H. a. ssp. pyramidatum, is native to North America.

 
       
 

Synonyms

 
 

Hypericum pyramidatum

 
       
 

Common Names

 
 

American great St. Johnswort

giant St. Johnswort

great St. Johnswort

 
       

 

 

 

 

 

 

 

 

Glossary

Clasping

Describing a leaf that wholly or partly surrounds the stem but does not fuse at the base.

 

Cyme

A branched, flat-topped or convex flower cluster in which the terminal flower opens first and the outermost flowers open last.

 

Elliptic

Narrowly oval, broadest at the middle, narrower at both ends, with the ends being equal.

 

Filament

On plants: The thread-like stalk of a stamen which supports the anther. On Lepidoptera: One of a pair of long, thin, fleshy extensions extending from the thorax, and sometimes also from the abdomen, of a caterpillar.

 

Obovate

Inversely egg-shaped, with the attachment at the narrower end.

 

Pedicel

In plants: the stalk of a single flower in a cluster of flowers. In Hymenoptera and Araneae: the narrow stalk connecting the thorax to the abdomen.

 

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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Greg Watson

 
 

Hypericum ascyron

I attached two pictures of Great St. Johnswort. I submitted the two pictures to Minnesota Wildflowers, Hypericum ascyron (Great St. Johnswort): Minnesota Wildflowers, and they agreed it was Hypericum ascyron. The pictures were taken along the Wagon Wheel Trail in La Crescent.

  great St. Johnswort  
           
        great St. Johnswort  
           
 
MinnesotaSeasons.com Photos
 
 

Plant

 
    great St. Johnswort   great St. Johnswort  
           
 

Inflorescence

 
    great St. Johnswort      
           
 

Flower

 
    great St. Johnswort      
           
 

Plant in late season

 
    great St. Johnswort      
           
 

Infructescence

 
    great St. Johnswort   great St. Johnswort  
           
 

Seed capsule

 
    great St. Johnswort   great St. Johnswort  
           

 

Camera

     
 
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slideshow

       
 
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  Greg Watson
7/10/2021

Location: Eagles Bluff Park, La Crescent, MN

I took these two pictures of a Jagged Ambush Bug at Eagles Bluff Park in La Crescent, MN on 9 September 2021.

great St. Johnswort

 
           
 
MinnesotaSeasons.com Sightings
 
   

 

 

Binoculars


Created: 9/15/2021

Last Updated:

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