St. John's Wort family (Hypericaceae)
This shrub is 1-3' tall, branching occasionally. The woody
branches near the base of this shrub have yellowish brown to reddish
brown bark that often becomes shredded into white strips or narrow
sheets. Young stems are light green, glabrous, and 4-angled. Pairs of
opposite primary leaves occur along the young stems. In addition,
there are often clusters of smaller secondary leaves near the axils of
the opposite primary leaves. These leaves are up to 2" long and 8 mm.
(1/3") across; they are linear-oblong to oblanceolate in shape and
their margins are entire (toothless) and revolute (rolled downward).
The upper leaf surface is bluish green to medium green, glabrous, and
sometimes glaucous, while the lower leaf surface is light green,
glabrous, and sometimes glaucous. All leaves are sessile or nearly so.
The upper stems terminate in corymbs or compound corymbs of 3-7
Each flower is about 1–1¼" across, consisting of 5 spreading
yellow petals, 5 light green or light yellow sepals, a light yellow
pistil with 5 styles (the latter are often united), and numerous
conspicuous stamens. The petals are broadly oblong or obovate in
shape, while the sepals are lanceolate; the petals are about twice the
of the sepals. The filaments of the stamens are light yellow, while the
anthers are medium yellow or golden yellow. The pedicels of the
flowers are up to ¾" long, light green, and glabrous. The blooming
period occurs from mid-summer to late summer, lasting about 1 month.
Afterwards, the flowers are replaced by seed capsules about 8 mm.
(1/3") long that are lanceoloid in shape and 5-lobed. The
interior of each seed capsule has 5 completely separated cells; there
are numerous seeds in each cell. These seeds are dark-colored,
narrowly oblongoid, and somewhat flattened. The woody root system is
shallow and spreading.
The preference is full sun, wet to moist conditions, and soil
containing calcareous sand or limestone. Shallow water is tolerated if
it is temporary. This shrub is winter-hardy to Zone 4.
& Habitat: Kalm's St. John's Wort occurs
in NE Illinois along Lake
Michigan, where it is native (see Distribution
In Illinois, this
shrub is rare and state-listed as 'endangered.' It is endemic to the
Great Lakes Region. Habitats include interdunal swales, borders of
small sandy ponds, moist to wet sandy meadows, and moist sand flats
(pannes). Outside of Illinois, Kalm's St. John's Wort occurs on
limestone flats (alvars). This shrub is found in high quality natural
areas. It is also cultivated occasionally in gardens because of its
Mostly various bees visit
the flowers, where they collect pollen. Nectar is not available as a
floral reward. Grundel et al. (2011) observed a leaf-cutting bee
(Megachile montivaga) and Halictid bees (Augochlorella
Lasioglossum pectorale) visiting the flowers of
Kalm's St. John's Wort.
Two oligophagous aphids suck the sap of this shrub: Aphis
Aphis hyperici. The caterpillars of an
oligophagous moth, Nedra
ramosula (Gray Half-spot), feeds on St. John's Wort species (Hypericum
spp.), while the caterpillars of two polyphagous moths, Eupithecia
miserulata (Common Pug) and Synchlora aerata
sometimes feed on the flowers (Lagos et al., 2012; Covell, 1984/2005;
Kalm's St. John's Wort is rarely browsed by White-tail
Deer. In places where this animal is abundant, this shrub has a
tendency to increase because of selective browsing (Bradstreet
2002). The leaves of St. John's Wort species are somewhat toxic to
domesticated farm animals, particularly those with white or thin fur.
These plants contain a toxin that increases sensitivity to the
ultraviolet radiation of sunlight, causing irritation of the skin.
Consumption of these plant species can also irritate the
gastrointestinal tract of these animals.
Border of a small sandy pond and a moist sandy meadow near Lake
Michigan in NE Illinois.
Populations of this small showy shrub appear to be increasing in some
protected areas of Illinois. Kalm's St. John's Wort can be
distinguished from most species of St. John's Wort (Hypericum
its woody lower branches; most species of St. John's Wort in Illinois
are entirely herbaceous. Compared to another shrubby species, Shrubby
St. John's Wort (Hypericum prolificum), Kalm's St.
John's Wort has more
narrow leaves (never exceeding 8 mm. across) and it has 5-celled seed
capsules, rather than 3-celled seed capsules. It is similar to another
shrubby species that is found in southern Illinois, Five-lobed St.
John's Wort (Hypericum lobocarpum). This latter
species has cymes with
a greater number of flowers (usually exceeding 7 flowers each) and its
flowers are smaller in size (about ¾" across).