American senna (Senna hebecarpa)
Cassia hebecarpa Fernald
Cassia hebecarpa var. longipila E. L. Braun
Senna hebecarpa var. longipila (E. L. Braun) C. F. Reed
CONFIRMATION STATUS: Pending confirmation.
TAXONOMY: The currently accepted scientific name of American
senna is Senna hebecarpa (Fernald) Irwin & Barneby. This is a striking
plant while in bloom, and it has attractive foliage. It is difficult to distin-
guish wild senna from Senna marilandica (Maryland senna), which has a
very similar appearance and also occurs in Facquier County. Generally,
wild senna has a slightly more northern distribution than Maryland senna,
but in many areas of the United States their ranges overlap, as they do in
Virginia. On wild senna, the pistils of the flowers have long white hairs,
while in Maryland senna these hairs are shorter and more appressed. The
nectary glands at the base of the compound leaves are also supposed to
shaped differently. In wild senna, these glands have a short stalk and are
club-shaped (although the shape of this 'club' can be variable), while the
glands of Maryland senna can be short-cylindric, rounded, or dome-shap-
ed, but they are without short narrow stalks. The seedpods of these two
species are also supposed to be somewhat different in appearance in rela-
tion to the number and shape of the seedpod segments.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS:
Habit: This native perennial plant is largely unbranched and up to 6' tall.
The stout central stem is light green, and slightly hairy in the upper stem
and at the base of the upper compound leaves.
Leaves: The compound leaves are even-pinnate with about 10-20 leaflets.
The medium to dark green leaflets are individually up to 2½" long and ¾"
across. Each leaflet is oblong, with smooth margins, and a pointed tip.
Near the upper base of a compound leaf is a small club-shaped gland; it is
ovoid or dome-shaped above a short stalk. This gland secretes nectar to
attract certain kinds of insects (see below for more information).
Flowers: From the axils of the upper compound leaves develop upright
acemes of yellow flowers. Each flower is about ¾" across; it has 5 pale
yellow sepals, 5 yellow petals, 10 stamens with black anthers, and a con-
spicuous pistil with long white hairs. The petals have a tendency to turn
white as they age, while the hairy pistil eventually develops into a seed-
pod. There are 3 upper petals and 2 upper petals in a flower; they have a
tendency to become curved and have a claw-like appearance. There is no noticeable floral scent.
Fruit/Seeds: The seedpods are about 4" long when fully mature; each
seedpod has 10-18 segments, and each segment is about as long as it is
across. Eventually, these seedpods become dark brown in appearance.
Roots: The root system consists of a central taproot and rhizomes. This
plant often forms vegetative colonies. It is not yet known if the plant has
the ability to fix atmospheric nitrogen.
REGENERATION PROCESS: American senna propogates itself
through reseeding; rhizome spread also contributes to propogation.
HABITAT TYPES: Habitats include moist meadows near rivers,
savannas, fens, pastures, fileds, and roadsides. It is generally found on
disturbed sites. It is often flourishes within the floodplain of rivers.
Occasionally, wild senna is found in flower gardens because of the
SITE CHARACTERISTICS: American senna prefers partial to full
sun, and moist to mesic conditions. A rich loamy soil is preferred. This
plant can become quite tall when the soil is fertile and moist; it may flop
over while the flowers and seedpods are developing. Foliar disease is not
a significant problem.
SEASONAL DEVELOPMENT: The blooming period is mid- to late
summer, which lasts about a month.
GENERAL DISTRIBUTION: American senna is a species primarily
restricted to the eastern United States and Canada. It occurs from Georgia
north to Maine, and westward to Tennessee, then north through the Illinois,
Wisconsin, Michigan, and into Ontario. It does not naturally occur in the
Prairie states, southwestern, far western or Pacific northwestern states,
and does not occur in Canadian provinces other than Ontario.
SKY MEADOWS DISTRIBUTION: To be determined.
IMPORTANCE AND USES: The flowers atttract bumblebees primar-
ily, which seek pollen from the anthers and possibly nectar. Halictid bees
also visit the flowers for pollen, but are less likely to achieve cross-pollin-
ation. The extra-floral nectaries, on the other hand, attract primarily ants
and a few other insects, including ladybird beetles. It is possible that these
insects protect the plant from other insects that would attack the foliage;
it has also been suggested that the extra-floral nectaries discourage ants
from robbing nectar from the flowers. The caterpillars of some sulfur
butterflies rely on Senna spp. as a source of food. This includes Eurema
nicippe (sleepy orange), Eurema lisa (little sulfur), and Phoebis sennae
eubule (cloudless sulfur). Mammalian herbivores usually avoid consump-
tion of the foliage, which has purgative properties. The seeds may be eat-
en by some upland gamebirds, including quail.
Several senna species are purgatives or laxatives depending on the dose.
The leaves and pods of the wild senna contain compounds called anthra-
quinones, which are powerful laxatives. For this reason cattle and other
herbivores avoid grazing the plants.
This is a stunning plant in bloom and has attractive foliage. It is popular
for meadow plantings and in native landscape gardens.
Crooked Run Valley