great St. Johnswort

not listed

NNR - Unranked

SNR - Unranked

not listed

FAC - Facultative

FAC - Facultative

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, 19⁄16″ to 3⅜″ (40 to 85 mm) long, and 11⁄16″ to 17⁄16″ (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 13⁄16″ 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 13⁄16″ (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, 5⁄16″ to ½″ (8 to 13 mm) long, and 3⁄16″ 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 19⁄16″ (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, ⅜″ to 13⁄16″ (9 to 30 mm) long, 3⁄16″ 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.

20″ to 78″ (50 to 200 cm)

Bright yellow

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.

July and August

The flowers are pollinated mostly by bumblebees.

Sources

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

Native

Common in eastern Minnesota

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.

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.

Plant

Inflorescence

Flower

Plant in late season

Infructescence

Seed capsule

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.