Description: This native perennial wildflower is
2-5' tall; it has an erect central stem and often develops short side stems in
the upper half. The central stem is light green to purple (usually the latter),
glabrous, and
glaucous. The alternate leaves are up to
8" long and 6" across (excluding the petioles), becoming gradually smaller as
they ascend the stems. The leaves are highly variable in shape; they can be
palmately lobed (with 3-5 lobes), deltoid, or ovate. The margins of these
leaves are dentate, undulate, or smooth. The upper surface of each leaf is
medium to dark green and glabrous. The petioles are as long as their leaf
blades or shorter. Both the stems and leaves contain a milky white latex. The
central stem and upper stems (if any) terminate in panicles of flowerheads.
Each panicle has a long ascending stalk (or peduncle) at its base, which
divides at its apex into 2-4 short spreading branches. From each branch,
several flowerheads droop downward from very short branchlets (or pedicels).
The light green branches of each panicle are hairless or finely pubescent. Each
flowerhead is about ¾" long and ½" across. The cylindrical base
of each flowerhead has 8 primary bracts (phyllaries) that are linear in shape,
pale purple-green, and hairless. There are also several secondary bracts at the
very bottom of the flowerhead that are much shorter than the primary bracts.
The upper flowerhead has 8-14 outer ray florets and no disk florets; the
petal-like ray florets spread outward widely when the flowerhead is in bloom.
These ray florets are pale purple, lavender, or white. The blooming period
occurs from late summer into the fall. A pleasant floral fragrance is often
present. Each floret is replaced by a small oblongoid achene with a tuft of
cinnamon-brown hairs; the achenes are distributed by the wind. The root system
is tuberous.
Cultivation: Preferred
growing conditions consist of light shade to dappled sunlight, average levels
of moisture, and a fertile loamy soil. Soil that is sandy or rocky is also
tolerated. The size of individual plants is strongly influenced by moisture
amounts, light levels, and soil fertility.
Range & Habitat: White Lettuce is occasional in
the northern half of Illinois, but rare or absent elsewhere (see
Distribution
Map). This species is more common in areas that lie north of the state.
Habitats include
rich mesic
woodlands, sandy woodlands, bluffs, wooded slopes, rocky ravines and the base
of cliffs in wooded areas, and woodland borders. White Lettuce can be found in
either oak or maple-basswood forests.
Faunal
Associations: The flowerheads are cross-pollinated by bumblebees,
which seek nectar. Even though the foliage of this species has a bitter taste,
it is sometimes browsed by White-Tailed Deer.
Photographic Location: A wooded sandstone ravine at
Portland Arches Conservation Area in west-central Indiana.
Comments: White Lettuce is one of five Prenanthes
spp. in Illinois; two of these species occur in prairies, while the other
three species occur in woodlands. The prairie species in this genus have narrow
spikes of flowerheads and lanceolate leaves. The woodland species in this genus
have spreading panicles of flowerheads and their leaves are often palmately
lobed (particularly the lower ones). White Lettuce can be distinguished from
the other woodland species in Illinois by its primary bracts: each flowerhead
has 8 primary bracts that are pale purple-green and hairless. In contrast, each
flowerhead of Prenanthes altissima (Tall White Lettuce) has 5 primary
bracts that are light green and hairless, while the flowerhead of Prenanthes
crepidinea (Great White Lettuce) has 12-15 primary bracts that are light
green and hairy. These species also differ in the number of outer ray florets
per flowerhead; the ray florets of White Lettuce are more likely to be pale
purple or lavender than those of Tall White Lettuce or Great White Lettuce.
Other common names of Prenanthes alba are Lion's Foot and Rattlesnake
Root.