Home » Plants » Hypericum mutilum

Dwarf St. John's Wort (Hypericum mutilum L.)

Also known as dwarf st. Johnswort.

Two subtaxa of this species are recognized; FSUS considers them varieties but FNA and POWO consider them subspecies.

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Summary
Range
Description
Similar Plants
Life Cycle
Fauna
Control
Relatives
Links
Photos

Photo © Rob John, CC BY 4.0.

↑Summary

A small annual or short-lived perennial of moist to wet sites, native to eastern North America.

↑Range - Expand

Legend	Color
Native
Introduced
Native or Not Present
Introduced or Not Present

This tentative map is based on our own research. It may have limited data on Canada and/or Mexico, and there is some subjectivity in our assignment of plants as introduced vs. expanded. Read more in this blog post.

↑Description & Identification

Dwarf St. John's wort is found in a wide variety of sunny to lightly shaded moist-to-wet habitats. Natural habitats include open floodplain forests, swamps, seeps and springs, marshes, wet meadows and wet to moist prairies, and shores of lakes, ponds, rivers, small depressions in open forests or barrens, or streams, especially where the shoreline has slightly receded during the growing season. Anthropogenic habitats include ditches, depressions in sandy paths, abandoned fields. In the east of its range where it is more abundant, it can also occur in wet spots in lawns and gardens.

It can grow on a wide range of soil pH but prefers acidic soils. In the west of its range, where it is less common, it restricted to acidic soils, often on rocky or especially on sandy substrates.

In the east, it is more common and occurs in a wider range of habitats, occuring in nearly any type of open wet area, and tolerating a wider range of soil textures, including sandy, rocky, silt, clay, and muck.

↑Similar Plants

Northern St. John's Wort (Hypericum boreale)
View - Compare

↑Life Cycle

Dwarf St. John's wort is an opportunistic annual to short-lived perennial that grows during the warm season. Seeds germinate in late spring when temperatures warm, and foliage of established plants emerges around the same time.

Its size, growth habit, and lifespan are highly dependent on conditions. The bloom period is long, often 2-3 months or even longer in parts of the south. The plant tends to open only a few flowers at a time, and then opens new flowers each day.

First-year plants usually flower and produce seeds, but often not as prolifically as established plants.

The entire plant, including foliage, stems, and seed capsules, turns a dramatic red color in fall.

We could not find information on the seed distribution mechanism, but the seeds are likely dispersed in part by water, and are also small enough to blow around in the wind in dry conditions. We could not find specifics on the duration of persistence in the soil seed bank, but a number of studies have found that this species is present in the soil seed bank and it may germinate from the seed bank in response to changes in water levels that expose new habitat that has not been suitable for a number of years.

As a small plant that does not reproduce vegetatively, plants can experience mortality from changing water levels, often in response to different year-to-year weather patterns, and can be killed if its habitat becomes too flooded. Plants are surprisingly drought resistant for a plant that primarily grows in wetlands, and towards the drier end of this species' conditions, it not usually killed by drought but rather by shading from taller, more aggressive plants as the soil becomes less saturated.

↑Faunal Associations

Mammalian herbivores usually avoid this plant. The flowers lack nectar, but attract a variety of small pollen-seeking bees, flies, and beetles. A large number of insects feed on this plant, mostly ones that specialize in the Hypericum genus.

↑Control

This plant is weedy and likely has invasive potential outside its native range; some other Hypericum species have become invasive when introduced to new areas. Due to this plant's small nature and potential to form a persistent seed bank it may be hard to remove once introduced, and it is thus important to avoid spreading this plant.

There are a large number of Hypericum species, mostly native but some introduced, that overlap with this one in range. No other plants in the Hypericaceae family occur in North America.