Rumex triangulivalvis (Danser) Rech.f.
Family: Polygonaceae
white dock, white willow dock, willow dock
[Rumex mexicanus var. triangulivalvis Meisn.,  more...]
Rumex triangulivalvis image
from USDA Plants website  
Rumex triangulivalvis image
University of Wisconsin - Madison (WIS-VP)  
Etymology: Rumex: the ancient Latin name for the docks or sorrels
Plants: perennial, to 40" tall, smooth forb often with several branches; taprooted
Leaves: flat, pale green or smooth, narrowly lance-shaped
Flowers: 6-parted, stalks jointed near the base; inflorescence a 4"-12" branched cluster with small leaves near the base of the few branches
Habitat: moist
Conservation Status: Native