Hypericum ascyron (Great St. Johnswort)
| Also known as: | Giant St. John's-wort |
|---|---|
| Genus: | Hypericum |
| Family: | Hypericaceae (St. John's-wort) |
| Life cycle: | perennial |
| Origin: | native |
| Habitat: | sun; moist; along shores, wet meadows, thickets |
| Bloom season: | July - August |
| Plant height: | 2 to 5 feet |
| Wetland Indicator Status: | GP: none MW: FAC NCNE: FAC |
| MN county distribution (click map to enlarge): |  |
| National distribution (click map to enlarge): |  |
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Detailed Information
Flower: 
![[photo of flowers]](/udata/r9ndp23q/yellow/great-st-johnswort_0719_114501.jpg)
Flowers are from 2 to 2½ inches across with 5 bright to golden yellow petals and many long yellow stamens with orange tips. In the center is a green pyramid shaped ovary with 4 or 5 red-tipped styles that are fused at the base. A flowers is at the end of a stem that arises from a leaf axil in the upper part of the plant.
Leaves and stem:
![[photo of leaves]](/udata/r9ndp23q/yellow/great-st-johnswort_0719_114538.jpg)
Leaves are up to 3 inches long and 1 inch wide, toothless and hairless, rounded at the base and slightly tapering to a point at the tip, with no leaf stem. There are glandular dots or streaks scattered on the surface. Attachment is opposite. The main stem is 4-angled on young plants, becoming 4-lined with maturity.
Fruit:
![[photo of fruit]](/udata/r9ndp23q/yellow/great-st-johnswort_0719_114553.jpg)
Fruit is a pyramid-shaped capsule with 5 chambers, about 1 inch long. It dries to brownish black and opens at the top when the seed is ripe.
![[photo of seed]](/udata/r9ndp23q/pd/hypericum-pyramidatum-seed.jpg)
Seed is cylindrical, dark brown, about 1 millimeter long, and resembles a tiny ear of corn.
Notes:
While the general shape of this flower resembles other St. John's-wort species, the size of the flower sets Great St. John's-wort apart from the rest. According to Flora of North America, there are at least 3 subspecies of Hypericum ascyron, but apparently only subsp. pyramidatum is present in North America. Formerly known as Hypericum pyramidatum, it is part of a variable species or species complex with a wide distribution throughout the northern hemisphere.
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More photos
Great St. John's-wort plant
garden grown Great St. John's-wort
ripe seed capsulesPhotos by K. Chayka taken at Wild River State Park, Chisago County. Photos courtesy Peter M. Dziuk taken in a private garden in Anoka County (it did not persist well there)
Comments
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2010-07-11 15:45:45
I think I have the ID correct.
on: 2011-07-14 13:58:55
Found today, 7/14/2011, in a remnant rock out-crop prairie. A small area, probably 15-20 plants on high ground. First time sighting.
on: 2014-07-28 22:01:14
Saw a few of these plants down along the river bottom in Clear Lake SNA. Too many invasives here though.
on: 2015-11-13 13:40:58
I asked the master gardners what I have in my back yard. It's so tall I wasn't sure if it is st johns wort, but they think it is, after looking at my pics.I think I'll collect some seeds for next year, if it's not too late. Just letting you know. Connie
on: 2015-11-13 19:07:56
We have some Hypericum pyramidatum in our yard. We love it, but it is actually becoming a little bit of a nuisance in the vegetable garden. :-)
on: 2016-07-03 09:16:47
There's about eight plants just about ready to open and blossom. The path goes through a wooded, swampy area and then to a almost field like situation where they made their home.
on: 2018-07-05 10:22:49
This wildflower is just starting to bloom in the grassy areas of the flood plain along the Mississippi River.
on: 2018-07-10 11:23:12
Noticed this plant this morning July 10 2018
on: 2018-07-24 14:24:12
I purchased this plant in St. Paul and the first year it was pretty tame, but this summer it is enormous and the bees are just crazy about the flowers. What an amazing plant!
on: 2018-07-25 20:40:07
It is Great St Johnswort
on: 2019-07-08 05:32:23
Found the Great St. John's wort for the first time today...old railroad prairie remnant...the flower head size and pyramid center was the easiest way to ID for me...also received ID from one of my 167K member plant ID groups.
on: 2019-07-14 09:26:50
Several plants east of the pond near the equestrian trailhead
on: 2019-07-21 17:30:49
I just found it growing in my field, next to my 25 year old prairie!!!
on: 2020-06-30 16:33:42
Great St. John's wort used to grow in a few sunny spots in the Boy Scout camp on Mirror Lake. It has been absent the past few summers, and I suspect mowing was the cause of its disappearance. Does anybody know where I could get seeds to start some at my cabin on Mirror Lake?
on: 2021-07-10 12:49:36
West end of the Lebanon Hills County Park Jensen Lake unit. This on July 10th.
on: 2021-07-17 14:05:17
My first time noticing these; thought they were jumbo buttercups at first. The bumblebees were going nuts over them.
on: 2023-07-13 15:50:40
At first I saw just one very tall yellow wildflower cluster poking up among a field of purple beebalm. But when I looked around more carefully, I found quite a few of these Great St. John's-wort plants blooming. This is the first time I've seen these flowers in our meadow.