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lady's thumb (Polygonum persicaria)




















lady's thumb
ladysthumb smartweed
spotted ladysthumb
Adam's plaster


Persicaria maculata (Raf.) Gray
Persicaria maculosa Gray
Persicaria persicaria (L.) Small
Persicaria ruderalis (Salisb.) C.F. Reed
Persicaria ruderalis (Salisb.) C.F. Reed var. vulgaris (Webb & Moq.)

   C.F. Reed
Persicaria vulgaris Webb & Moq.
Polygonum dubium Stein
Polygonum fusiforme Greene
Polygonum minus auct. non Huds.
Polygonum minus Huds. var. subcontinuum (Meisn.) Fernald
Polygonum persicaria L. var. angustifolium Beckh.
Polygonum persicaria L. var. ruderale (Salisb.) Meisn.
Polygonum puritanorum Fernald


CONFIRMATION STATUS: Pending confirmation.


TAXONOMY: The currently accepted scientific name for lady's thumb

is Polygonum persicaria L. This species is often listed as Persicaria

maculosa on the Internet and in texts and field guides, including the Flora of Virgnia.


NATIVE STATUS: Introduced, United States and Canada.




Habit: This summer annual plant (considered a weed of horticultural,

agronomic, and nursery crops) is about ½–2' tall) although they may

reach 3 1/2 feet in height), generally erect, but stems may be procum-

bent, decumbent, or ascending. Individual plants may sprawl. The stems

are usually light green (often reddish in color), round, glabrous or slight-

ly pubescent and and swollen at the nodes. Stems simple or branched,

without obvious ribs, glabrous or appressed- pubescent.


Leaves: The alternate leaves are up to 6 inches long and 1 - 1 1/4 inches
across, although usually smaller. They are lanceolate or linear-lanceolate,
hairy on the upper surfaces (older leaves are usually only slightly hairy),
smooth along the margins, and sometimes slightly ciliate. Each leaf has a
short petiole or it is nearly sessile. A thin membranous sheath called an
ocrea encircles the stem at the base of each leaf petiole. The light brown,
cylindric ocrea's of lady's-thumb have a few longitudinal veins and stiff

hairs arising from the top of the ocrea, which are approximately 2 mm

long. The upper surface of a leaf often has a black smudge or purple spot

in the middle of the leaf that is oval or triangular-shaped which resembles

the mark of a lady's thumb, thus the name of this weed. This smudge may

be dark and conspicuous or faint and barely perceptible.


Flowers: Each upper stem terminates in 1 or 2 spike-like racemes of flow-

ers; there are often shorter racemes that develop from the axils of the up-

per leaves on peduncles. Each raceme is about ½–1½" long, more or less

erect, and oblongoid in shape from the crowded whorls of small flowers.

The sepals of the flowers may be pink, red, greenish white, or purple,

even on the same raceme; usually pink flowers are the most common.

Each flower is about 1/8" long and shy to open; it consists of 5 sepals, 6

stamens (usually), a style that is divided into 2-3 parts toward the middle,

and no petals. The sepals are not glandular-punctate, and the stamens are

not exerted beyond the sepals. There is no noticeable floral scent.


Fruit/Seeds: Each flower is replaced by a seed that is ovoid, flattened or
slightly 3-angled, black, and shiny.


Roots: Lady's-thumb has a fibrous, shallow root system doesn't produce rhizomes. Roots often arising from proximal nodes. There are no rhizomes

and stolons. This plant often forms colonies, partic- ularly in disturbed

wetland areas, or it may occur in drier areas as scattered plants.


REGENERATION PROCESS: Lady's thumb propogates itself by re-



HABITAT TYPES: Habitats include marshy areas, edges of streams and
drainage canals, mudflats, roadside ditches, moist weedy meadows, vacant
lots, fallow fields and edges of cultivated fields, edges of yards and gardens,
moist areas along railroads, and waste areas. This species prefers disturbed
areas, but can invade higher quality wetlands to a limited extent.


SITE CHARACTERISTICS: Lady's thumb prefers full sun or partial sun,
wet to mesic conditions, and fertile soil with organic matter. However, this
adaptable plant will also grow in light shade and poor soil containing clay,
gravel, or sand.


SEASONAL DEVELOPMENT: The blooming period can occur from

late spring to early fall (May into October); a colony of plants will typical-

ly bloom for 1-2 months during the summer.


GENERAL DISTRIBUTION: Lady's thumb is found in all states and
provinces of the United States and Canada, except in the Northwest
Territories and Nunavut.




IMPORTANCE AND USES: The nectar of the flowers attracts Halictid
bees, wasps, and Syrphid flies primarily. Short-tongued bees suck nectar
or collect pollen; flies suck nectar or feed on pollen; and other insects suck
nectar. Less comon visitors include small butterflies and bumblebees.
Halictid bees also collect pollen occasionally. The foliage is eaten by the

caterpillars of some Copper butterflies and several species of moths, while

the flowers and fruit are eaten by the caterpillars of the gray hairstreak

butterfly. Japanese beetles are also quite fond of the foliage of this and

other smartweeds. Flea beetles that feed on the foliage or roots include Chaetocnema concinna (brassy flea beetle), Systena frontalis (red-headed

flea beetle), Disonycha pensylvanica, and Disonycha conjugata. Mam-

malian herbivores rarely feed on the foliage of lady's thumb because the

foliage is pungent, peppery, and slightly bitter. However, white-tailed

deer may chomp off the tops of young plants upon occasion. The seeds

of smartweeds are very popular with waterfowl and granivorous song-

birds. The seeds of lady's thumb, in particular, are eaten by birds in both

upland and wetland habitats.


Lady's thumb has been considered a medicinal plant. Native Americans
used the leaves in treatments of stomach pains and poison ivy. They also
rubbed the plant on their horses as an insect repellant. The Cherokee,
Chippewa, and Iroquois prepared simple or compound decoctions of lady's
thumb, which they used as dermatological, urinary, gastrointestinal, and
veterinary aids, for heart medicine, and as an analgesic. Lady's thumb is
still used against diarrhoea and infections.


Fresh leaves have been used to staunch bleeding. The leaves and young
shoots may be eaten as a palatable and nutritious leaf vegetable.



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