Northern Prairie Wildlife Research Center
Aquatic and Wetland Vascular Plants of the Northern Great Plains
15. Polygonaceae, the Smartweed Family
1. Polygonum L. -- Smartweed, knotweed, tear-thumb
10. Polygonum ramosissimum Michx.-- Bushy knotweed
Erect, sparingly to usually freely branched, taprooted annual 2-9 dm tall, the
stems strongly ribbed. Leaf blades elliptic to mostly narrowly elliptic
or nearly linear, 8-40 mm long, 2-15 mm wide, acute to obtuse, often revolute,
cuneate and jointed at the subsessile or short-petioled base; ocreae
membranous with 2 acute lobes, soon lacerate and breaking into brownish fibers.
Flowers in axillary positions near the tips of branches, 1-few per axil;
calyx 5(6)-parted, 3-4.5 mm long, the lobes united for about 1/3 of their
length or less, green with yellowish, whitish or slightly pinkish margins, the
outer 3 cucullate and enclosing the inner lobes; stamens usually 5, included;
style branches 3. Achenes dark brown, dull to shiny, sharply trigonous,
mostly 3-3.5 mm long and enclosed by the calyx, those produced later in the
season often larger and distended beyond the calyx; pedicels mostly enclosed
by the ocreae, 1-3 mm long. Jul--Sep. Shores and exposed flats, especially where
alkaline; common; (Newf. to B.C., s to VA, IN, OK and CA). P. prolificum
Some other polygonums of the knotweed group are sometimes found in the same
habitats as P. ramosissimum, but are more characteristic of disturbed
upland habitats. Most typical of this group is P. arenastrum Jord.
ex Bor. (formerly included in P. aviculare L.) which differs from P.
ramosissimum in its spreading to erect habit; calyx lobes pink-margined,
more or less flat and not cucullate at the tips; achene unequally trigonous,
with 2 convex sides and 1 narrower concave side. Another is P. erectum,
a spreading plant with broadly elliptic leaves; calyx united near the
middle and constricted above to appear bottle-shaped.
Previous Species -- Polygonum punctatum Ell.--
Return to Family -- Polygonaceae -
The Smartweed Family
Next Species -- Polygonum sagittatum L.--