Weeds, Insects & Diseases

Smartweed [Polygonum scabrum]



Description

Smartweed plants can grow up to 30" tall, with tapered leaves.


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Propagation, emergence and growth

Smartweed is an annual that reproduces by seed only.Cotyledons elliptic, attached at 180 degrees from each other when seen from above. True leaves alternate, elliptic to lanceolate, with matted hairs on undersides of first 5 to 7 leaves. Papery she...


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Distribution

Smartweed can be found throughout the country.


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Description

Smartweed plants can grow up to 30" tall, with tapered leaves.

Propagation

Smartweed is an annual that reproduces by seed only.

Seedling

Cotyledons elliptic, attached at 180 degrees from each other when seen from above. True leaves alternate, elliptic to lanceolate, with matted hairs on undersides of first 5 to 7 leaves. Papery sheath around stem where leaves join to it.

  • Smartweed

Mature Plant

Stems erect or ascending to prostrate in open areas, branched, usually 1-1/2 to 4 feet tall at maturity, but can grow up to 6 feet. Swollen nodes at leaf axils where stems are encircled by a membranous sheath. Upper edge of sheath has minute bristles, only seen under magnification. Lower stems smooth, hairless; upper stems rough or gummy.





Leaves alternate, elliptic to lanceolate, 1 to 6 inches long, smooth edges, bottom 5 to 7 leaves hairy, matted underneath. Upper leaves usually hairless, with round, yellow, glandular dots underneath, leaving a yellow smudge when rubbed over a white paper. Leaves narrow into stalk, sometimes have a dark splotch marking in center.

Root Structure Description:

Taproot, branched.

Flowers Description:

Pink to white to green, without petals, in dense, spikes 1/2 to 4 inches long, at stem ends and in leaf axils. Green smartweed flowers in shorter, wider spikes than pale smartweed. Flowers July through September. Seeds lens-shaped, black shiny.

Distribution

Smartweed can be found throughout the country.

Similar Species

Green and pale smartweeds are very similar to lady's-thumb because of the matted hairy undersides of the bottom 5 to 7 leaves, the yellow glandular dots ont he undersides of upper leaves, and the lack of long hairs on the upper edge of the membranous sheaths.