Polygonum americanum (Fisch. & C.A. Mey.) T.M. Schust. & Reveal

Jointweed

Polygonum americanum plant

Family - Polygonaceae

Stems - Multiple from base, erect to ascending, translucent lepidote (use a lens to see), suffrutescent at the base, herbaceous above, resembling a small cedar when not in flower.

Polygonum americanum stemStem and leaves.

Leaves - Alternate, thin, scalelike to subulate, sessile, to +1cm long, +/-1mm broad, translucent lepidote (use a lens to see), subsucculent, often lighter colored and rounded at the apex. Ocrea with a lighter green to yellowish apical margin.

Polygonum americanum leavesLeaves.

Inflorescence - Dense terminal and axillary racemes to +/-4cm long. Pedicels white, glabrous, 3-4mm long. Each flower arising from the axil of a reduced leafy bract. Bracts scalelike, enclosing the stem, acute to acuminate at the apex, with a whitish apical margin, glabrous, with white speckling (use a lens to see). The apex of one bract enclosing the base of the leaf above it.

Polygonum americanum inflorescenceInflorescence

Flowers - Perianth whitish. Outer two sepals white with a green midrib, cupped at the apex, 2mm long, +1.7mm broad, glabrous, often somewhat folded, broadly ovate. Inner sepals 3, white, spreading, orbicular, 2-3mm long and broad, glabrous. Stamens +/-8, erect, exserted. Filaments white, glabrous, broadened in the basal 1/2, +/-2mm long. Anthers white to pinkish, .6mm long. Ovary superior, white, 3-angled, glabrous, white with minute pinkish tips. Receptacle with a reddish rim surrounding a green nectary.

Polygonum americanum flowersFlowers in-situ.

Polygonum americanum flowerFlower close-up.

Flowering - July - October.

Habitat - Dry sandy ground.

Origin - Native to U.S.

Other info. - This attractive little species is uncommon in Missouri, only being found in a handful of counties which contain parts of Crowleys Ridge. It can also be found in Iron County in one or two select locations.
The plant is very easy to identify because of its large numbers of small white flowers and because it resembles a small cedar or juniper when not in flower. Nothing else in the states flora really resembles it.
P. americana would make a fine garden plant if sandy, acidic conditions could be provided. It grows well from seed.
This species has also been called Polygonella americana.

Photographs taken at the Holly Ridge Conservation Area, Stoddard County, MO., 6-14-03 (DETenaglia); also at Sand Prairie Conservation Area, Scott County, MO, 7-30-2015 (SRTurner).


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