Asian lady's thumb is a slender annual of shady, damp woodland edges, native from Japan, Korea, and China south and west to Southeast Asia and the Himalayas. Its pink flowers sit in thin, loosely flowered spikes. The look-alike weed that has spread across much of the eastern US is a close relative, Oriental lady's thumb (Persicaria longiseta).
Appearance
- Growth form
- An annual about 8–28 in (20–70 cm) tall. The base sprawls or leans and can root at the nodes, while the upper stem stands up.
- Leaves
- Oval to long-oval leaves about ¾–4¼ in (2–11 cm) long, tapering to a long point. A papery sheath wraps the stem at each leaf base and is fringed with long bristles.
- Flowers
- Small pinkish to white flowers in slender, sparsely flowered spikes. In Japan it blooms from August to October.
- Fruit
- A shiny black, three-sided seedlike fruit about 1/12 in (2 mm) long.
Look-alikes
Asian lady's thumb has broader, egg-shaped leaves that narrow to a long, tail-like tip, and thin spikes with flowers spaced far apart. Oriental lady's thumb has narrower, lance-shaped leaves and denser spikes; it's the one you're likely to find in the eastern US.
Why they get mixed upThey look alike, and the same scientific name has been used for both.
Where it lives
- Typical habitats
- Shady woodland edges
- Damp forest floors
- Range
- Native to Japan, Korea, China (including Taiwan), the southern Kuril Islands, and Russia's Primorye region, and south and west through mainland Southeast Asia and the Philippines to the Himalayas, Assam, and Bangladesh.
- Preferred conditions
- Prefers partly shaded spots with moist soil.
Name and classification
- About the name
- The name Persicaria posumbu has sometimes been used in a broad sense that also covers the weedy Oriental lady's thumb, which first showed up near Philadelphia around 1910. That weed is now usually treated as its own species, P. longiseta, so information about the US weed doesn't necessarily apply to the Asian woodland plant described here. Some plant lists record P. posumbu as introduced in New Jersey and New York, but those reports may really be the look-alike P. longiseta. Don't confuse either one with plain "lady's thumb" (Persicaria maculosa), a different smartweed.
Conservation
- IUCN Red List
- NENot EvaluatedNot yet assessed
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