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A Forager’s Year

No. 83

Smartweeds

Persicaria lapathifolia (also P. maculosa, P. pensylvanica, P. extremiorientalis)

pale smartweed, lady’s thumb, Pennsylvania smartweed

Leaves & tender stems young leaves and tender shoot tips

Drawing: Britton & Brown, Illustrated Flora (1913)

No modern safety review found. No extension, government, poison-center or botanic-garden page was found that reviews eating pale smartweed, lady’s thumb or Pennsylvania smartweed leaves; NC State has no page for pale smartweed or lady’s thumb and lists no food or poison use for Pennsylvania smartweed, and the safety sources found cover only cattle grazing and the lookalike water pepper.

Find
Common in the right habitat
Effort
Quick kitchen prep
ID risk
Careful
Origin
mixed
Safety marks
  • Spray risk
Uses
  • Eat raw / salad
  • Cooked vegetable / soup
  • Pesto & sauces

Season

  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec

in season peak

Picking: No park we checked allows it. Anywhere else, ask whoever owns or runs the land. See Where you may pick.

What these mean

Find

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

ID risk

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Native or not, and the invader stars

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Safety marks and flags

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger, recorded near DC (an iNaturalist sighting within 25 km, a DC street tree, or a Smithsonian listing for DC) and looking like the part you eat. Other lookalikes are still listed, marked “not recorded near DC” or as not looking like the part you eat. Deadly means a source says eating it may be fatal or calls it deadly, or NC State rates it high severity with life-threatening symptoms (sources sometimes disagree; for example Virginia creeper). Each plant’s Lookalikes list says how to tell them apart; “harmless (may be edible)” lookalikes are listed so you know a mix-up isn’t dangerous. Cook first: cooking is needed for safety (for daylilies it is a precaution, not a sourced requirement). Eat in moderation: a source says to limit quantity or frequency (for example oxalates in sorrels and dock, ginkgotoxin, safrole). Spray risk: a source says the plant is commonly treated with herbicide in parks or lawns (invasive control, lawn weeds) or, for ginkgo, sprayed to stop fruiting. Contamination: a source says the plant concentrates pollutants. Each plant’s Safety flags list gives the details and sources.

Seasons

Start, peak and end are given in thirds of a month: early, mid or late. A plant counts as in season for a month if it is in season at any point in that month. Some greens and roots have a second window, in spring or fall; their page shows each window. A season that runs across New Year is shown as one window.

What it looks like

Smartweeds are summer annual weeds of the buckwheat family with alternate, lance-shaped leaves, stems that look like miniature bamboo, and small pink or white flowers packed into spikes (Forager Chef). The stems are often reddish and swollen at the joints, and a thin sheath wraps the stem at the base of each leaf (Eat The Weeds). Lady’s thumb usually has a dark, thumbprint-like mark in the middle of the leaf, and its sheath is hairy with a fringe of hairs along the top (Ontario weed guide; Massey University). Pale smartweed looks very similar, but its flower spikes are longer, paler and nodding, its leaves often have no dark mark, and its sheath has no fringe (Eat The Weeds; Massey University). Pennsylvania smartweed, which overlaps with lady’s thumb, has short, upright spikes of rose-pink flowers, a sheath without a fringe and sticky, hairy stems, and only occasionally a dark leaf mark (Forager Chef; Eat The Weeds; NC State). Pale and Pennsylvania smartweed are native, while lady’s thumb was introduced from Europe (Digital Atlas of the Virginia Flora; Forager Chef). Forager Chef finds lady’s thumb and pale (dock-leaved) smartweed mild, with a subtle green-bean taste and a gently slippery texture once cooked, and calls them a decent vegetable, though not the equal of lamb’s quarters, amaranth or nettles; older plants can be slightly astringent. Edible Wild Food calls lady’s thumb foliage peppery and slightly bitter, and Forager Chef suggests that reports of a spicy taste may come from confusion with water pepper. Foraging Texas calls lady’s thumb a delicious potherb.

Safety

No poisoning of people from eating these smartweeds is reported in the sources checked, but no extension or poison-center page reviews them as food. Lookalike: water pepper, which Massey University says is often confused with lady’s thumb. Its leaves are strongly peppery (NC State) and its foliage acrid (Massey University), and Massey’s poisonous-plants database says it may cause contact dermatitis and gut irritation and lists people among those affected. Water pepper’s flowers are pale pink to whitish, often with a greenish tinge, and less tightly clustered than lady’s thumb’s, and its leaves tend not to have as distinct a dark mark (Massey University); lady’s thumb and pale smartweed taste mild, while water pepper is hot (Forager Chef; Eat The Weeds). Eat The Weeds says to keep your fingers away from your eyes after handling older or peppery plants, or they will smart. Plants For A Future, a plant database, says many members of the genus contain oxalic acid, are best eaten in moderate amounts and lose some of it in cooking, and that some members have been reported to cause sensitivity to sunlight; no safety source checked confirms either for these species. In Australia, a government district veterinarian linked cattle deaths from liver failure to smartweeds, pale smartweed and a related species, grazed at the edges of drying dams after hot weather; an earlier feeding trial did not reproduce the illness, and no source reports harm to people eating the leaves. North Dakota State University lists smartweed among plants that can build up nitrate, a concern for livestock. Foraging Texas advises cooking rather than eating the leaves raw, because bacteria from the water the plant grows along can contaminate them. Washington State University lists a lawn herbicide for smartweeds, so avoid lawns and borders that may have been sprayed.

Lookalikes

Safety flags

Safety marks and flags: what this means

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger, recorded near DC (an iNaturalist sighting within 25 km, a DC street tree, or a Smithsonian listing for DC) and looking like the part you eat. Other lookalikes are still listed, marked “not recorded near DC” or as not looking like the part you eat. Deadly means a source says eating it may be fatal or calls it deadly, or NC State rates it high severity with life-threatening symptoms (sources sometimes disagree; for example Virginia creeper). Each plant’s Lookalikes list says how to tell them apart; “harmless (may be edible)” lookalikes are listed so you know a mix-up isn’t dangerous. Cook first: cooking is needed for safety (for daylilies it is a precaution, not a sourced requirement). Eat in moderation: a source says to limit quantity or frequency (for example oxalates in sorrels and dock, ginkgotoxin, safrole). Spray risk: a source says the plant is commonly treated with herbicide in parks or lawns (invasive control, lawn weeds) or, for ginkgo, sprayed to stop fruiting. Contamination: a source says the plant concentrates pollutants. Each plant’s Safety flags list gives the details and sources.

ID risk
Careful
Why
Irritant lookalike: water pepper (Persicaria hydropiper), which Massey University says is often confused with lady’s thumb and which may cause contact dermatitis and gut irritation. Water pepper has pale pink to whitish, often greenish, less tightly clustered flowers, leaves that tend not to have as distinct a dark mark, and a leaf sheath without lady’s thumb’s fringe of hairs (Massey University), and its leaves are hot (NC State), while these smartweeds taste mild (Forager Chef).
Handling hazards
Irritant sap/pulp (minor)
Soil risk
higher
ID risk: what this means

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Handling hazards: what this means

Stings, thorns, irritating or phototoxic sap, staining hulls and spiny husks, with a severity: minor = brief discomfort; moderate = rash or blisters lasting days; serious = burns, scarring or medical care possible.

Soil risk: what this means

Based on the part you eat, following the urban-soil lead guidance on the Field safety page: higher for greens, shoots and roots; moderate for flowers; low for fruit, nuts and sap.

Field safety for every outing (poison ivy, ticks, soil, and more)

When to pick

Starts
mid May
Peak
early Jun–late Jul
Ends
mid Sep

Smartweeds are summer annuals. Lady’s thumb sprouts early in spring (Ontario weed guide), and Forager Chef, in Minnesota, sees smartweeds appear as soon as the soil warms, around June. Only young, tender growth is picked, and older plants can be slightly astringent (Forager Chef). Lady’s thumb flowers from June to mid-September (Edible Wild Food), and Massey University says it dies off in late autumn. Around DC most sightings are logged from August to October, when the plants are in flower (iNaturalist). No source gives dates for the DC area, so all boundaries are estimates.

How the dates were worked out

Every start, peak and end was re-checked in October 2026. “Sourced” means a source opened during the check states that timing for the DC or Mid-Atlantic area. “Estimated” means no source states it exactly; the reason, the evidence and the source links are under “How the dates were worked out” on each plant’s page. Peaks are often estimated, because few sources name a peak. iNaturalist evidence means research-grade sightings near DC, by month, of the plant at that stage (for example, in fruit). iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Season basis: estimated: start, peak, end

Start

estimated: No source dates the start for the DC area; mid May allows for spring sprouting and the warmer soil of the DC area compared with Minnesota, when DC sightings begin to rise.

Peak

estimated: No source names a best time; early June to late July is when plants are young and growing fast, before most of them flower.

End

estimated: No source gives an end date; mid September is when flowering plants are older and tougher, though some tender tips remain until the plants die back in autumn.

Evidence

start: Ontario weed guide: lady’s thumb 'Germinates and emerges early in the spring.' Forager Chef (Minnesota): smartweeds 'are summer annuals that seem to appear the instant the soil warms up around June in Minnesota.' DC iNaturalist research-grade sightings by month: April 3, May 9, June 16. | peak: Forager Chef: 'Only the young growth is harvested.' and 'Older ones I’ve had can be slightly astringent'. Edible Wild Food: 'Lady’s thumb flowers typically occur from June to mid-September.' DC iNaturalist flowering annotations by month: July 0, August 1, September 15, October 2. | end: Forager Chef: 'Older ones I’ve had can be slightly astringent'. Edible Wild Food: flowers 'from June to mid-September.' Massey University: 'It is a summer annual, dying off in late autumn.' Eat The Weeds: 'If flowers from about May to October, depending on your climate.'

Where to look

Damp, sunny, disturbed ground such as stream and lake banks, ditches, gardens and vacant lots; logged most along the C&O Canal towpath and Four Mile Run and at the Wheaton Branch stormwater ponds, but no listed park allows picking it, so gather on private land with the owner’s permission, where no herbicide is used.

Habitats
disturbed ground & waste places, vacant lots, old fields & meadows, floodplain & stream-valley forest, wetlands, marshes & pond edges
Habitats: what this means

Listed where the plant’s own sources place it in that habitat. “Disturbed ground & waste places” means a cited source places it on disturbed areas, sites, soil or ground, on waste places or waste ground, on construction or abandoned building sites (old home sites count), on rubble or in strip mines. When the source gives examples of the disturbed places, at least one example must be of that kind. Examples that do not count: natural or forestry disturbance (treefall gaps, fire, windthrow, flood scour, old riverbanks and creeks, clear-cuts); roadsides, railroads and rights-of-way; and abandoned fields, pastures and farmland, which are “Old fields & meadows”. “Vacant lots” only where a source says vacant or empty lots.

Most-logged places

None of the most-logged places allows picking.

Ask first: rules unclear or not checked

  • Wheaton Branch Stormwater Ponds (Montgomery County land)

    9 sightings · Legal to pick: unknown · see them on iNaturalist

    Montgomery County stormwater land, not M-NCPPC parkland; picking rules not checked. iNaturalist’s outline also takes in nearby homes, churches and homeowners'-association land.

No picking here (4 places)
  • C&O Canal NHP (towpath, Georgetown to Great Falls MD and beyond)

    15 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: the C&O Canal compendium covers only edible fruits, nuts, berries and mushrooms, and NPS parks can never designate leaves, flowers, roots or sap.

  • Four Mile Run stream valley (Arlington/Alexandria)

    11 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Arlington County park rules (flora shall not be removed or disturbed) and Alexandria’s permit rule both apply.

  • Mount Vernon Trail

    8 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: GW Memorial Parkway sites (incl. Great Falls VA, Theodore Roosevelt Island, Dyke Marsh) designate nothing for gathering.

  • Sligo Creek Stream Valley Park

    7 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Montgomery/Prince George’s parks (M-NCPPC) ban harvesting vegetation without a permit.

Most-logged places: what this means

The places with the most research-grade iNaturalist sightings within 25 km of downtown DC (re-counted in October 2026 over every named place, campuses, condominiums and private grounds included), each marked legal to pick or not. A sighting inside several named places counts once, for the smallest of them, but a sighting inside a National Park Service park never counts for a private, campus or unchecked place. iNaturalist shows where people walk and log plants, not true abundance. Private campuses, condominiums, museums, estates and utility land (Pepco’s power-line land near Sligo Creek) are marked “no” (pick only with the owner’s permission); public university campuses, city parks and other places whose picking rules were not checked (county stormwater land, the U.S. Capitol Grounds, Greenbelt’s North Woods, federal facilities such as the National Zoo) are “unknown”. A place needs at least 2 sightings, so plants with very few sightings have no places. At-risk plants (butternut, nannyberry, American chestnut, ramps, riverbank goldenrod) get places like every other plant; each page says why the plant is at risk and gives any advice its sources give. For some places, mostly Rock Creek Park, the iNaturalist map shows more sightings than the count here, because a map link cannot leave out exactly the sightings credited to another place. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Ways to use it

  • young tips boiled 1 to 2 minutes until just tender, then served with soft butter and a pinch of salt (Forager Chef)
  • boiled 8 to 10 minutes as a potherb and served with butter, roasted garlic or bits of bacon (Foraging Texas)
  • mild, non-peppery leaves in salads (Eat The Weeds)
  • chopped into soups and cooked rice dishes, anywhere mild leafy greens are used (Forager Chef)
  • mixed with stronger or bitter greens, as in Greek horta with lemon and oil or greens cooked with garlic and chili (Forager Chef)
  • Japanese-style gomae salad, boiled, chilled and dressed with crushed sesame seeds or nuts and soy sauce (Forager Chef)
  • harvest only the tender tips and leaf clusters a few inches long, pinched off or cut with scissors (Forager Chef)
  • harvest by taste: mild leaves are eaten as greens, peppery ones only as a seasoning (Eat The Weeds)

Keeping

Use within 2–3 days, or blanch 2 minutes and freeze.

Use within
within a few days
Keeps fresh
2–3 days refrigerated, wrapped in a damp paper towel inside a perforated plastic bag (general guidance for leafy greens; University of Maine). Forager Chef says tips rinsed in cold water, spun dry and refrigerated have stayed fresh for up to three weeks for him.
Keeping basis
general guidance for its type

Ways to keep it

  • Freeze as researched: blanch & freeze; canning: n/a (not shelf-canned)

    NCHFP: water-blanch greens 2 minutes (collards 3), cool, drain and pack with 1/2-inch headspace. No tested process names smartweed; this is the general method for greens, best for cooked dishes.

Canning: what this means

Shelf-stable canning, three levels. Lab-tested: a lab-tested recipe from the National Center for Home Food Preservation (NCHFP) or Oregon State covers this fruit and product, or a generic recipe for its kind (the line says so, for example chokeberry). Extension recipe: a published Extension recipe (University of Alaska Fairbanks, written for Alaska species; University of Maine’s dandelion jelly), or a process that is safe only with a pH meter; follow it exactly, never improvise. No tested recipe: refrigerate or freeze, don’t can. “Hot-bottled syrup” = maple and walnut syrup, which keep when bottled hot at full syrup density. The Canning line names the exact product each source covers, for example “whole berries” or “juice”; a product not named there (such as juice from a berry with only a whole-berry recipe) has no tested recipe.

Keeping basis: what this means

“Specific to this plant” or “general guidance for its type” (for example NCHFP guidance for leafy greens applied to a wild green).

Nutrition

Not researched: in October 2026, only the calendar’s plants of the month and chicory leaves were researched.

Native or not

Origin
mixed
Native range
P. lapathifolia and P. pensylvanica: native to North America (USDA PLANTS); P. maculosa: Europe (Forager Chef), introduced in North America (USDA PLANTS); P. extremiorientalis: Japan, China, Korea and the Russian Far East (iNaturalist)
Virginia invasive rank
not listed
Maryland invasive status
not listed
Native or not, and the invader stars: what this means

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Virginia DCR, Virginia Invasive Plant Species List (effective September 2024), verbatim: "Under the DCR Invasive Species Assessment Protocol, approved by the Virginia Invasive Species Working Group, January 2024, species were ranked as exhibiting high, medium or low levels of invasiveness based on their threat to natural communities and native species. Invasiveness rank is higher for species that: • Alter ecosystem processes, such as succession, hydrology or fire regime. • Are capable of invading undisturbed natural communities. • Cause substantial impacts on rare or vulnerable species or natural communities or high-quality examples of more common communities. • Are found widely distributed and generally abundant where present. • Disperse readily to new areas. • Are difficult to control." The list also states: "The list is for educational purposes only and has no regulatory authority."

Maryland Department of Agriculture, Maryland Prohibited Invasive Plant Law and Regulations page, verbatim: "Plants on the Maryland Prohibited Invasive Plant List may not be added to stock after the effective date and should not be sold after their phase-out period ends."

No official DC invasive plant list was found.

How the ratings were set

Find
Common in the right habitat Estimate 329 = 313 research-grade iNaturalist sightings within 25 km + 370 needs-ID sightings counted at 3% (313 of the 8,943 research-grade Persicaria sightings here are pale smartweed, lady’s thumb, Pennsylvania smartweed or Far Eastern smartweed) + 3 'cultivated' (planted) sightings (rule A); that is tier 2 by count (rule B). Rule D does not apply: the Digital Atlas of the Virginia Flora says of pale smartweed "Frequent in the Piedmont; infrequent in the mountains and Coastal Plain.", which is not a statement that it is rare, and the same sentence calls it frequent in the Piedmont, part of the circle; the same atlas calls lady’s thumb and Pennsylvania smartweed "Frequent throughout." Final tier 2.
Effort
Quick kitchen prep Pinch off the tender tips and boil them 1 to 2 minutes (Forager Chef), or 8 to 10 minutes as a potherb (Foraging Texas); mild leaves raw in a salad (Eat The Weeds) would be a 1, though Forager Chef finds smartweeds tough raw.
Find: what this means

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort: what this means

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

Sources

34 sources, each linked to the original.

  1. Rock Creek Park Superintendent’s Compendium National Park ServiceBacks up: picking rules
  2. 36 CFR 2.1 - Preservation of natural, cultural and archeological resources Legal Information Institute, Cornell Law School (text of federal regulation)Backs up: picking rules
  3. Persicaria pensylvanica (Pennsylvania Smartweed) NC State Extension Gardener Plant ToolboxBacks up: description, habitat
  4. Persicaria lapathifolia (L.) Gray (Dock-leaf Smartweed, Pale Smartweed) (Digital Atlas of the Virginia Flora) Virginia Botanical Associates (Digital Atlas of the Virginia Flora)Backs up: description, habitat, findability, native or invasive status
  5. Persicaria maculosa Gray (Lady’s-thumb) (Digital Atlas of the Virginia Flora) Virginia Botanical Associates (Digital Atlas of the Virginia Flora)Backs up: description, habitat, findability, native or invasive status
  6. Lady’s Thumb (Polygonum persicaria) Edible Wild FoodBacks up: description, season
  7. Weed identification guide for Ontario crops: Lady’s thumb Ontario Ministry of Agriculture, Food and AgribusinessBacks up: description, season, habitat
  8. New Zealand weeds database: Willow weed (Persicaria maculosa) Massey University (New Zealand)Backs up: description, season, safety, effort & ID risk, safety details
  9. Lady’s Thumb Foraging TexasBacks up: description, uses, safety, habitat
  10. Lady Thumbs (Green Deane) Eat The WeedsBacks up: description, uses, season, safety, habitat
  11. Lady’s Thumb and Other Edible Smartweeds (Alan Bergo, 2024) Forager ChefBacks up: description, uses, season, safety, habitat, native or invasive status, keeping
  12. iNaturalist research-grade observations of Persicaria lapathifolia + P. maculosa + P. extremiorientalis within 25 km of downtown DC iNaturalistBacks up: findability
  13. Persicaria pensylvanica (L.) M. Gomez (Pennsylvania Smartweed, Pinkweed) (Digital Atlas of the Virginia Flora) Virginia Botanical Associates (Digital Atlas of the Virginia Flora)Backs up: habitat, findability, native or invasive status
  14. Bulletin #4180, Vegetables and Fruits for Health: Greens University of Maine Cooperative ExtensionBacks up: keeping
  15. Freezing Greens (Including Spinach) National Center for Home Food Preservation (University of Georgia)Backs up: keeping
  16. USDA PLANTS Database: Polygonum lapathifolium (= Persicaria lapathifolia) (POLA4), native status USDA NRCSBacks up: native or invasive status
  17. USDA PLANTS Database: Polygonum persicaria (= Persicaria maculosa) (POPE3), native status USDA NRCSBacks up: native or invasive status
  18. USDA PLANTS Database: Polygonum pensylvanicum (= Persicaria pensylvanica) (POPE2), native status USDA NRCSBacks up: native or invasive status
  19. iNaturalist taxon record: Persicaria extremiorientalis (Far Eastern smartweed) iNaturalistBacks up: native or invasive status
  20. Virginia Invasive Plant Species List (effective date: September 2024) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: native or invasive status
  21. Maryland Prohibited Invasive Plant Law and Regulations (Maryland Prohibited Invasive Plant List, updated January 2026; additions effective July 15, 2026; 'Next Plants To Be Assessed' 2026-2027) Maryland Department of Agriculture, Plant Protection & Weed ManagementBacks up: native or invasive status
  22. Non-Native Invasive Terrestrial Plant Species in the State of Maryland (updates approved through the April 18, 2024 MISC meeting) Maryland Invasive Species CouncilBacks up: native or invasive status
  23. Plant Invaders of Mid-Atlantic Natural Areas, Field Guide (Swearingen & Fulton, 2022; successor to the NPS/USFWS 5th ed., 2017) Mid-Atlantic Invasive Plant Council / Passiflora Press (hosted by Bugwood/Mid-Atlantic Invaders Tool)Backs up: native or invasive status
  24. Invasive Plants in the District DC Department of Energy & EnvironmentBacks up: native or invasive status
  25. Polygonum persicaria (Spotted ladysthumb) Plants For A Future (plant database)Backs up: safety
  26. Polygonum lapathifolium (Curlytop knotweed) Plants For A Future (plant database)Backs up: safety
  27. Smartweed (Persicaria spp.) poisoning in cattle (Ian Lugton, District Veterinarian, 2013) Flock & Herd (New South Wales district veterinarians)Backs up: safety
  28. V839, Nitrate Poisoning of Livestock North Dakota State University ExtensionBacks up: safety
  29. New Zealand weeds database: Water pepper Massey University (New Zealand)Backs up: safety, effort & ID risk, safety details
  30. Water pepper (Polygonum hydropiper), poisonous plants database Massey University (New Zealand)Backs up: safety, effort & ID risk, safety details
  31. Persicaria hydropiper (Water-pepper) NC State Extension Gardener Plant ToolboxBacks up: safety, effort & ID risk, safety details
  32. Weeds: Smartweeds (HortSense fact sheet, reviewed 2026) Washington State University ExtensionBacks up: safety, safety details
  33. iNaturalist research-grade observations of pale smartweed, lady’s thumb, Pennsylvania smartweed and Far Eastern smartweed within 25 km of Washington, DC, by month (all observations) iNaturalistBacks up: season
  34. iNaturalist research-grade observations of the same smartweeds within 25 km of Washington, DC, by month (flowering annotation) iNaturalistBacks up: season