common St. John's wort (Hypericum perforatum)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

COMMON NAMES:
alien St. John's-wort
St. John's wort
klamathweed
common St. John's wort
klamath weed
common St. Johnswort
common Saint John's-wort

 

SCIENTIFIC SYNONYMS: There are no scientific synonyms for
Hypericum perforatum.

 

CONFIRMATION STATUS: Pending confirmation.

 

TAXONOMY: The currently accepted scientific name of common St.
John's wort is Hypericum perforatum L. This species is usually in bloom
during the summer solstice (dedicated to St. John), hence the common
name. Common St. John's wort is unique among the Hypericum spp. (St.
John Worts) because it has black dots along the margins of its flower pet-

als. The species Hypericum punctatum (dotted St. John's Wort) has black

dots and streaks along the interior of its flower petals, while other St.

John's worts have petals without any black dots. Common St. John's wort
branches more than dotted St. John's wort, and it has larger flowers (about

¾" across) than the latter (about ½" across). The seeds of common St.

John's wort have a surface that is somewhat roughened by small pits, while

the seeds of many native St. John's worts have a smooth surface.

 

NATIVE STATUS: Introduced, United States and Canada.

 

GENERAL BOTANICAL CHARACTERISTICS:

 

Habit: This introduced perennial plant is 1–2½' tall, branching frequently.

The round stems are hairless and light green; the larger stems have a pair

of small longitudinal ridges.

 

Leaves: The opposite leaves are about 1" long and 1/3" across. They are
oblong, hairless, and sessile. The surface of these leaves is perforated by
numerous translucid dots, and there are often scattered black dots along
the margin of the lower surface.

 

Flowers: The upper stems terminate in flat-headed clusters of several

flowers (cymes). Each flower is about ¾" across, consisting of 5 yellow

petals, 5 green sepals, 3 styles, and numerous stamens (more than 20).

There are scattered black dots along the margins of the petals. The sepals

are lanceolate and much smaller than the petals. The petals turn brown

and persist near the seed capsules, rather than falling to the ground.

 

Fruit/Seeds: Each 3-celled seed capsule is well-rounded at the base, be-

coming conical at its apex. Each cell of the seed capsule contain numerous

seeds, which are oblong, flattened, and black. The surface of each seed is

somewhat roughened by numerous small pits, rather than smooth.

 

Roots: The root system is rhizomatous, and produces numerous basal off-

shoots around the base of the plant.

 

REGENERATION PROCESS: Common St. John's wort propogates
itself by reseeding and vegetatively through basal offshoots and rhizomes.

 

HABITAT TYPES: Habitats include mesic to dry sand prairies, barren
savannas, grasslands, and steppes, degraded weedy meadows, open wood-
lands, riverbanks, stony and grassy slopes, gravelly areas along railroads
and roadsides, pastures and abandoned fields, and sterile waste areas.
There is a preference for disturbed areas in dry or well-drained habitats
with little vegetation. Common St. John's wort was introduced from

Europe as a garden plant.

 

SITE CHARACTERISTICS: Common St. John's wort prefers full sun
and mesic to dry conditions. Common St. John's wort adapts to virtually
any kind of soil that contains loam, sand, or gravel; there is a preference
for soil that is alkaline. This plant can spread aggressively by forming
vegetative colonies, and can be difficult to get rid off.

 

SEASONAL DEVELOPMENT: The blooming period occurs from
early to mid-summer and lasts about a month.

 

GENERAL DISTRIBUTION: Common St. John's wort is found
throughout most of the United States (excepting Florida and Ala-

bama, New Mexico and Utah) and Canada (excepting Saskatchewan

and Alberta).

 

SKY MEADOWS DISTRIBUTION: To be determined.

 

IMPORTANCE AND USES: Bumblebees and other kinds of bees visit
the flowers to collect pollen. Occasionally, Syrphid flies and beetles may

feed on the pollen, although they are less effective at pollination. The

showy flowers may attract other kinds of insects (e.g., wasps and butter-

flies), but they are vainly seeking nectar, which the flowers don't produce.

The caterpillars of the butterfly Strymon melinus (gray hairstreak) feed

on the seed capsules of Hypericum spp. (St. John's Worts), while the cater-

pillars of the moth Nedra ramosula (gray half-spot) feed on the foliage.

Mammalian herbivores are not attracted to common St. John's wort as a

food plant because it can cause a photosensitive reaction (particularly in

light skinned animals) and gastrointestinal distress.

 

 

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