This annual with rather weak, often nodding, stems is an introduced plant from south Asia. When erect it may reach 2.5 feet in height. Stems are hairless and may be unbranched or have a few branches originating near the base. The sessile or short petioled, alternate, lance-shaped to elliptical leaves are 3-4 inches in length by 1 inch wide.(A) Many, but not all leaves may have a purplish chevron-like blotch or “thumbprint” near the middle of the upper leaf. The membranous sheath (ocrea) which encircles the stem at the base of each leaf has long bristles on its margins.(C,D) The pink flowered, slender racemes are fairly dense above, but flowers are more widely spaced below often with the basal group quite widely separated from the others.(E) Flowers often have prominent bristles at their base, especially the lower ones.(E) Fruit is a shiny, black, three-angled seed.
Moist, disturbed sites. Locally common at Neale Woods just beyond the bridge over Rock Creek and on the west portions of Missouri River Ecology Trail beyond the bridge. It has not yet been found at Fontenelle Forest but is to be expected there.
Alternate names for Bristly Lady’s Thumb (Persicaria cespitosa) include Oriental Lady’s Thumb, Creeping Smartweed and Tufted Smartweed. Most of the leaves on the Creeping Smartweed (Persicaria cespitosa) we have seen and photographed at Neale Woods have had only a faint chevron or none at all. It should be noted that many plants may possess a distinct chevron or ‘thumbprint’ similar to Lady’s Thumb (Persicaria maculosa), another smartweed with pink flowers which is considerably more common at FF and NW. P. cespitosum racemes tend to be more slender, the flowers more widely spaced and the bristles on the sheaths more prominent. Pennsylvania smartweed (Persicaria pensylvanica) also has pink flowers, but no blotches on the leaves or bristles on the sheaths.
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