Persicaria lapathifolia (L.) Delarbre
Family - Polygonaceae
Stems - To 2m tall, glabrous.
Leaves - Alternate, glabrous, to 30cm long, 6cm wide, typically lanceolate, with impressed veins on the adaxial surface near the midrib. Ocrea not fringed with cilia and glabrous.
Inflorescence - Terminal, loose, panicles and axillary racemes. Each flower cluster to 8cm long(tall), 3-9mm thick, nodding.
Flowers - Small(2-3mm long), creamy white to slightly pinkish, dense in cluster.
Flowering - July - October.
Habitat - Moist soils, disturbed sites, gravel bars, roadsides, railroads.
Origin - Found in U.S. and Eurasia. Probably introduced in North America.
Other info. - This plant can get quite tall and is easily distinguished by the nodding racemes of the panicle. The leaves sometimes have a dark splotch in the center but this is not as common or pronounced as in the much smaller P. persicaria.
Photographs taken along the Current River, Shannon County, MO., 8-17-03 (DETenaglia); also at Columbia Bottoms Conservation Area, St. Charles County, MO, 8-4-2016 (SRTurner).