Rumex stenophyllus Ledeb.
Family - Polygonaceae
Habit - Perennial herb with thickened rootstock.
Stems - Ascending to erect, 1 to a few, to 1 m, usually branched, glabrous, with ocreae at nodes. Ocreae tan, papery, tearing and often absent at maturity.
Stem and node.
Stem and leaves.
Leaves - Basal and alternate. Blades of main leaves 15-25 cm long, 2-7 cm wide, mostly more than 4 times longer than wide, oblong-lanceolate or lanceolate, those of the uppermost leaves shorter and narrower, unlobed, the margins entire or nearly so, usually undulate and somewhat crisped, rarely flat or nearly so, angled to truncate at the base, sharply pointed at the tip, the surfaces glabrous.
Inflorescences - Terminal, occupying the upper 1/2 or more of the plant, relatively narrowly paniculate (the branches ascending or occasionally curved upward), relatively dense at fruiting.
Flowers - In whorled fascicles of 20-25 flowers, the stalks 3-8 mm long, 1.0-1.5 times as long as the fruiting perianth, arched downward or nodding. Inner whorl of tepals becoming enlarged to 3.5-5.0 mm long and 3-5 mm wide (excluding the teeth) at fruiting, with relatively broad wings, broadly ovate to ovate-triangular. Tepals with 8-20 conspicuous triangular to narrowly triangular teeth along the wing margins, these 0.2-1.5 mm long, much shorter than the width of the undivided portion, the surfaces with a prominent network of nerves. Tubercles 3, all similar in size, covering less than 1/2 of the width of the tepal, glabrous, smooth to faintly and finely wrinkled; the outer whorl spreading.
Fruits - 2-3 mm long, 1.0-1.5 mm wide, light reddish brown to reddish brown or brown.
Flowering - May - June.
Habitat - Riverbanks, bottomland forests, railroads, roadsides.
Origin - Native to Eurasia
Other info. - This species is uncommon in Missouri, found so far only in four counties divided between the far eastern and northwestern portions of the state. Species of Rumex can be difficult to differentiate. Various aspects of the fruiting tepals, such as their size, nature of the marginal fringing, if any, and whether the tubercles differ in size, are important in identification.
Photographs taken at Marais Temps Clair Conservation Area, St. Charles County, MO, 6-20-2017 (SRTurner).