Persicaria longiseta (Oriental Lady's-thumb)

Plant Info
Also known as: Bristly Lady's-thumb, Bristly Knotweed, Low Smartweed, Creeping Smartweed
Genus:Persicaria
Family:Polygonaceae (Buckwheat)
Life cycle:annual
Origin:Asia
Status:
  • Weedy
Habitat:part shade, sun; moist disturbed soil; shorelines, floodplain forest, woods, ditches, waste places, roadsides
Bloom season:July - October
Plant height:1 to 3 feet
Wetland Indicator Status:GP: none MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 5-petals Cluster type: raceme Cluster type: spike

[photo of flowers] Slender spike-like racemes up to 1½ inches long at the tips of branching stems, sometimes in the upper leaf axils. There may be gaps in the lower part of the cluster (interrupted) but not in the upper part (uninterrupted). Flowers are pink, about 1/8 inch long, with 5 tepals (petals and similar sepals). At the base of the flower is a short sheath (ocreola) with bristly hairs that are often as long as the flower, sometimes longer.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate, thin, lance-shaped, up to 3 inches long and to 1¼ inches wide, toothless, hairless except for short cilia-like hairs around the edge and sometimes on major veins on the underside. Leaves are stalkless or nearly so, and do not have a dark blotch on the upper surface, but may have a faint spot.

[photo of ocrea] At the base of the leaf is a brown, membranous sheath (ocrea) that surrounds around the stem, has pale ribbing, and bristly hairs up to ½ inch long around the edge. Stems are hairless, green to red, prostrate but rising at the tips (decumbent) or ascending, often rooting at the nodes in the lower plant, creating colonies.

Fruit: Fruit type: seed without plume

Fruit is a shiny, smooth, dark brown to black, 3-sided seed that is less than 1/8 inch long.

Notes:

Oriental Lady's-thumb, sometimes known as Polygonum caespitosum var. longisetum, most closely resembles Lady's-thumb (Persicaria maculosa), which does not have the long bristles in the flower cluster, a trait only P. longiseta has. P. maculosa also has hairs only about 1/8 inch long on its ocrea compared to ½ inch on P. longiseta, and it always has a distinct dark blotch on the upper leaf surface, which P. longiseta lacks. P. longiseta has only been collected twice in Minnesota, back in 1993 in two southeast counties. It's not been recorded since but that doesn't mean its presence in Minnesota hasn't expanded. Au contraire, we spotted a fairly large roadside colony along Hwy 95 near Afton in Washington County. We suspect this is another under-reported weed, probably overlooked due to its similarity to the rather common P. maculosa.

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More photos

Photos courtesy Peter M. Dziuk taken near Afton, Washington County.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: luise - Minnetonka
on: 2015-10-25 12:36:12

After the flood of a few years back and living on the back waters of Minnehaha Creek, I have a yard with a spot about 10x20 feet patch of this Lady's thumb. My plants look like your first Dziuk picture. They pop up in my squash garden, raspberry patch and many empty patch in the yard. It has many flowers from branches that go to one stem. Plant can grow to 20 inches, I guess. They started around the birch tree...lots of moisture

I am not a well educated yard anything. But these buggers are like creeping charlie. I need to pull many out, hours and hours of work, or they will take over most of the yard. Save me.

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