Polygonum pensylvanicum L.

Polygonum pensylvanicum plant

Family - Polygonaceae

Stems - To +80cm tall, herbaceous, erect to ascending, widely branching at or near base, mostly glabrous but glandular pubescent near inflorescence, from big taproot.

Polygonum pensylvanicum stemPortion of upper stem showing glandular pubescence.

Leaves - Alternate, petiolate, sheathing. Ocrea glabrous, NOT fringed. Petiole to 1.5cm long, glabrous. Blade typically lanceolate, acuminate, glabrous (or scabrous just on midrib), punctate below, entire, to 15cm long, +3cm wide, slightly decurrent on petiole. Margins antrorse strigillose.

Polygonum pensylvanicum ocreaOcrea.

Polygonum pensylvanicum leaves

Inflorescence - Terminal and axillary racemes to 4-5cm long, 1.5cm thick. Peduncles glandular pubescent. Ocreolae NOT fringed. Pedicels to 2.5mm long, glabrous.

Polygonum pensylvanicum inflorescence

Flowers - Perianth segments 5, 3mm long, 2.1mm broad, broadly elliptic, glabrous, whitish-pink to white. Stamens 10, mostly included to barely exserted. Filaments to -3mm long, glabrous. Anthers pale pink to pinkish-rose. Styles 2, joined for about half their length, free above, whitish, glabrous. Stigmas globose. Ovary green, glabrous, compressed, rotund, .9mm in diameter. Mature achene brown, slightly 3-sided, -3mm in diameter, shiny, glabrous, with concave sides.

Polygonum pensylvanicum flowerFlower close-up.

Flowering - May - October.

Habitat - Moist to wet locations, gravel bars, disturbed sites, waste ground, roadsides, railroads.

Origin - Native to U.S.

Other info. - The perianth of this species is variable between pink and white. Steyermark breaks the species apart into 3 varieties and 3 forms depending on leaf and stem pubescence and flower color. The plant described above is P. pensylvanicum var. laevigatum f. laevigatum.
P. pensylvanicum var. laevigatum f. albineum Farw. has pure white flowers.
Variety pensylvanicum has either leaves which are appressed pubescent below OR peduncles which are glabrous instead of the usual glandular pubescent.
Regardless of which variety or form you find, this species resembles another species, P. bicorne Raf., which is much less common in Missouri.

Photographs taken off Hwy 60, Carter County, MO., 8-31-03.


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