Weed Description: A summer
annual weed of horticultural, agronomic, and nursery crops that may reach 3 1/2 feet in
height. Pennsylvania smartweed is distributed throughout the United States.
Seedlings: Cotyledons are elliptic to lanceolate in outline, whit
hairs along the margins. First true leaves are alternate, lanceolate in outline, and
hairy on the upper surfaces.
Leaves: Arranged alternately
along the stem, lanceolate to elliptic in outline, approximately 2 to 6 inches long and 1
1/4 inches wide. Older leaves are usually only slightly hairy. Leaves taper to
short petioles, which have an ocrea that encircles the stem. Leaves often, but not
always, have a purple spot in the middle of the leaf.
Stems: Branched, often reddish in
color and swollen at the nodes. A thin membranous sheath called an ocrea encircles
the stem at the base of each leaf petiole. The ocrea's of Pennsylvania smartweed do
not have any hairs arising from the the ocrea, as is the case with many other similar
Fruit: A black achene.
Flowers: Flowers are clustered
in terminal spikes at the ends of stems. Individual flowers are small and usually
pink in color but can occasionally be white.
Characteristics: The elliptic to lanceolate leaves with a purple spotted 'lady's
thumb' print in the middle and distinctive ocrea are all characteristics that help to
distinguish Pennsylvania smartweed from other similar weeds. Ladysthumb (Polygonum persicaria) is very similar in
appearance and growth habit, but has stiff hairs on the ocrea that are approximately 2 mm
long unlike that of Pennsylvania smartweed. Tufted
Knotweed (Polygonumcaespitosum var. longisetum) is also
similar in appearance and growth habit, but has hairs on the ocrea that are much longer (5
to 10 mm) than those of ladysthumb.