This perennial wildflower is 1-3' tall and usually unbranched. The
erect central stem is light green (less often purplish green),
4-angled, and either glabrous or minutely pubescent. Pairs of opposite
leaves about 2-4" long and ½-1½" wide occur at intervals along this
stem. The leaves are lanceolate or elliptic in shape, and sparsely
dentate along their margins (usually about 3-5 teeth on each side);
some of the leaves may have margins with fewer or no teeth.
Usually, the upper
leaf surface is medium green and glabrous, while the lower surface is
pale green and glabrous. Sometimes the leaf surfaces are minutely
pubescent, particularly along their lower central veins. In bright
sunlight, some of the leaves may acquire reddish coloration,
particularly along their central veins. The leaves taper gradually to
somewhat abruptly into petioles up to 1" long.
Dense clusters of
nearly sessile flowers occur along the middle to upper leaves; they are
whorled around the central stem and located above the petioles of the
leaves. Each flower consists of a light green calyx with 4-5 teeth, a
white short-tubular corolla with 4-5 lobes, 2 slightly exerted stamens,
and a pistil. The corolla is 3-5 mm long, while the calyx is 2-3 mm.
long and its teeth are narrowly
triangular. The blooming period occurs from mid-summer into the fall,
lasting about 2-3 months. Usually, relatively few flowers are in bloom
at the same time. Each flower is replaced by 4 nutlets about 1.0-1.5
long; these nutlets are 3-angled and obovoid-oblong in shape; their
surfaces are tuberculate (bumpy), particularly along their outer
margins. The root system is rhizomatous or stoloniferous; it usually
forms tubers. Small colonies of plants are often produced from the
rhizomes or stolons.
The preference is partial sun, wet to moist conditions, and soil
containing some sand and organic material, although other soil types
The native Stalked Water Horehound is
most areas of Illinois, where it is uncommon to occasional (see
Habitats consist of openings in floodplain
woodlands, swamps, soggy thickets and meadows, and low areas along
pools of water. Sometimes Stalked Water Horehound is found on rotting
tree trunks that have fallen over, and in mossy areas near the bases of
trees. The wetlands where this wildflower occur are often partially
shaded, protected from prevailing winds, and somewhat sandy.
There are no records of floral pollinators
Water Horehound, but they are probably similar to those of Lycopus
(Common Bugleweed). These pollinators consist
including long-tongued bees, short-tongued bees, wasps, and flies. The
tubers of Stalked Water Horehound and other tuberous Lycopus spp.
eaten by muskrats. Because the foliage is bitter-tasting, it is rarely
bothered by mammalian herbivores.
sandy swamp at the Heron Boardwalk in Vermilion County, Illinois. The
photographed plants were growing near a rotting log along a pool of
The flowers of Stalked Water Horehound are a
little larger and showier than the flowers of other Lycopus spp.
Illinois. The species in this genus are similar in appearance and they
are rather difficult to distinguish. Stalked Water Horehound has
petioled leaves with 3-5 teeth (less often 0-2 teeth) along their
the calyces of its flowers have narrowly triangular teeth. These
calyces exceed 2 mm. in length (including their teeth). In contrast,
in this genus have more teeth along their leaf margins, or their lower
leaves are lobed; and some species have shorter toothed calyces (less
mm. in length).