Pennsylvania Smartweed (Polygonum pensylvanicum) The leaves are arranged alternately along the stem, lanceolate to elliptic in outline, approximately 2 to 6 inches long and 1.25 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. 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), which is not native, 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.