This biennial wildflower is 4-12" tall, developing one or more leafy
stems from a taproot. These stems are erect, ascending, or sprawling;
they are light green, glabrous, angular, and usually
(although they may branch after the blooming period). Numerous
alternate leaves occur along each stem that are ascending to widely
spreading. Individual leaves are narrowly oblong or narrowly
oblong-oblanceolate and smooth along their margins; they are medium
green, glabrous, and sessile. Each leaf has a single prominent vein.
Each stem terminates in a spike-like raceme of purple flowers about
¾-4" in length. The central stalk of the raceme is light green to
purplish green and glabrous. Each flower is about ¼" long and across
when it is fully open, consisting of 3 petals, 5 sepals, several
inserted stamens, and a pistil with a single style. Two sepals are
enlarged, rosy pink to purple, and petaloid, forming a pair of lateral
wings. The remaining three sepals are smaller in size, light green to
purple, and ovate in shape. The 3 petals form a fringed tubular
structure that surrounds the stamens and style; they are rosy pink to
purple, often becoming more white toward their tips. The short
glabrous pedicels of the flowers are light green to
purple, slender, and
often nodding. Sometimes a few cleistogamous (self-fertile) flowers
toward the base of the raceme; they are bud-like and inconspicuous. The
blooming period occurs from early to mid-summer and lasts about 3
weeks. Only a few flowers are in bloom at the same time. Afterwards,
they are replaced by 2-celled seed capsules; each cell of a capsule
contains a single hairy seed. In addition to the above-ground flowers,
Purple Milkwort also produces cleistogamous flowers along underground
stems. The root system consists of a taproot.
The preference is full or partial sun, mesic to dry
conditions, and sandy soil.
The native Purple Milkwort is
occasional in sandy areas of the
half of Illinois, while in the southern half of the state it is absent
Habitats consist of upland sand prairies,
upland sandy savannas, interdunal flats and stabilized sand dunes, and
abandoned sandy fields. Habitat destruction, off-road vehicle use, and
trampling by park visitors in heavily populated areas are threats to
current populations of this plant.
Information about floral-faunal
relationships for Purple
Milkwort and other milkworts (Polygala
) is limited. The flowers of
Purple Milkwort are cross-pollinated by Masked bees (Hylaeus spp.
other small bees. Even though Purple Milkwort and other milkworts have
bitter foliage, they are sometimes grazed by White-Tailed Deer and
possibly other herbivores (Martin et al., 1951/1961).
A stabilized sand dune with
scattered oak trees
at Indiana Dunes State Park in NW Indiana.
The flowers of Purple Milkwort are small, but attractive and
ornamental, resembling miniature orchid flowers if they are examined
closely. It can be
distinguished from other milkworts (Polygala
) in Illinois by its
slender racemes with distinct pedicels and purple flowers. Other
milkworts have stout floral spikes with pedicels that are absent or
hidden, or they have slender racemes
with white flowers. Pink
) is something of an exception, but it has
floral spikes that are more dense and leaves that are scale-like. In addition,
the tubular structure of its flowers is more elongated than the
corresponding structure of Purple Milkwort's flowers. Another common
name of Polygala
is Racemed Milkwort.