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A Forager’s Year

No. 87

Canada lettuce

Lactuca canadensis

wild lettuce, tall lettuce

Flowers, buds & pollen tender tops with unopened flower clusters (cooked)

Drawing: Britton & Brown, Illustrated Flora (1913)

Find
Patchy
Effort
Quick kitchen prep
ID risk
Careful
Origin
native
Safety marks
  • Toxic lookalike
  • Cook first
Uses
  • Cooked vegetable / soup

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

A tall native wild lettuce that lives two years, usually unbranched and 3 to 8 feet tall, with a smooth stem that is light green or reddish green, sometimes streaked with purple and often with a whitish bloom (Illinois Wildflowers). The leaves are up to 10 inches long and clasp the stem; the larger ones are deeply lobed and the smaller ones shallowly lobed or not at all, and a few fine hairs may run along the midrib underneath (Illinois Wildflowers). Cut leaves and stems give a white milky sap that quickly turns brownish or yellowish (Forager Chef; Foraging Texas). The tops are the tender upper stem with its narrow cluster of unopened flower buds, cut before the cluster branches out; after that they turn tough and can be unpleasant to chew (Forager Chef). Foraging Texas says the flower stalks are tender before the flowers open. The small yellow dandelion-like flower heads open in late summer or early fall (Illinois Wildflowers). Forager Chef calls Canada lettuce the best of all the wild lettuces for eating.

Safety

Canada lettuce has a bitter white milky sap. The Illinois Natural History Survey (University of Illinois) says the plant can cause digestive and nervous system problems, and advises cooking the young shoots and changing the first boiling water to remove the milky sap and bitter taste. Eight people in Iran were hospitalized after eating a European wild lettuce (Lactuca virosa) raw as a vegetable, some of them in large amounts, with symptoms such as dizziness, vomiting, blurred vision and hallucinations; all recovered, and the doctors reported that the severity depended on the amount eaten (BMJ Case Reports, 2009). No poisoning by Canada lettuce itself is reported in the sources checked, but cook it as the Illinois Natural History Survey advises and eat moderate amounts; Nature’s Restaurant, a foraging guide, also says to eat only small amounts, because large amounts have a slight narcotic effect. Nebraska Extension says some wild lettuces have caused lung damage (pulmonary emphysema) in cattle that ate large amounts of young plants. The tops are cut as the plant gets ready to flower, the stage at which Plants For A Future, a plant database, says the narcotic substance in wild lettuces is strongest; no safety source confirms this for Canada lettuce, so cook the tops and eat moderate amounts. Garden lettuce, in the same genus, can cause allergic skin rashes from its bitter compounds lactucin and lactucopicrin, and people allergic to other plants of the daisy family, such as chicory, chamomile or sunflowers, may cross-react (Anais Brasileiros de Dermatologia, 2025). Toxic lookalike: American burnweed (fireweed), which NC State says is often confused with wild lettuce, contains pyrrolizidine alkaloids (PROSEA), a group of liver toxins (Molecules, 2019). Burnweed’s flower heads have no petals and are white or cream, and its crushed leaves can smell unpleasant (NC State), while Canada lettuce has yellow flowers and white milky sap in its leaves and stems (Illinois Wildflowers). Harmless lookalikes: prickly lettuce has bluer leaves with a comb-like row of prickles under the whitish midrib (Nature’s Restaurant; Illinois Wildflowers); woodland lettuce has blue-white flowers and leaves deeply lobed all the way up the stem (Foraging Texas); tall blue lettuce is much hairier (Forager Chef), and NC State calls it not edible; sow thistles have a smooth midrib with no prickles or hairs (NC State; Forager Chef); dandelion has a smooth, rounded midrib and never forms a leafy central stalk (Forager Chef; Nature’s Restaurant); and chicory has blue flowers (Forager Chef). Hairy lettuce, a close relative listed as critically imperiled in Maryland (Maryland Department of Natural Resources), is hard to tell from Canada lettuce (Go Botany; Smithsonian checklist).

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
Toxic lookalike: American burnweed, which NC State says is often confused with wild lettuce and which contains liver-toxic pyrrolizidine alkaloids (PROSEA; Molecules, 2019). Burnweed has hairy stems, crushed leaves that can smell unpleasant and petal-less white or cream flower heads (NC State); Canada lettuce has a smooth stem, white milky sap in its leaves and stems, and yellow flowers (Illinois Wildflowers). The other lookalikes (prickly, woodland, tall blue and hairy lettuce, sow thistles, dandelion, chicory) are harmless; prickly lettuce has a comb of prickles under the midrib (Nature’s Restaurant).
Soil risk
moderate
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.

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
early Jun
Peak
late Jun–mid Jul
Ends
early Aug

No source gives picking dates for the DC area. The tops are cut while the flower cluster is still tight, before it branches out (Forager Chef), or, as Foraging Texas puts it, while the flower stalks are tender before the flowers open. Canada lettuce blooms in July, August and September (Lady Bird Johnson Wildflower Center), in late summer or early fall for about 3 to 4 weeks (Illinois Wildflowers). Around DC, the few iNaturalist sightings marked as budding fall between the third week of June and late July.

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; early June allows for the growing flower stalks before the first budding sightings logged around DC in the third week of June.

Peak

estimated: No source names a best time; late June to mid July covers the DC-area budding sightings, while the flower cluster is still tight.

End

estimated: No source gives an end date; early August is when DC-area plants are flowering, after which the tops are too tough.

Evidence

start: Forager Chef: 'As wild lettuce plants grow, the flower stalk becomes rigid (tough) to support the plant, but you can bend the growing top to see where it’s tender like asparagus.' Foraging Texas: 'The flower stalks are tender before the flowers open'. iNaturalist, verifiable sightings within 25 km of DC annotated 'flower budding': first in week 25 (about the third week of June). | peak: iNaturalist, verifiable sightings within 25 km of DC annotated 'flower budding': weeks 25 (2), 26 (1) and 29 (1); none at other times. Forager Chef: the tops can be cut 'anytime before the individual flowers begin to branch off of the panicle.' | end: Lady Bird Johnson Wildflower Center: 'Bloom Time: Jul, Aug, Sep'. Illinois Wildflowers: 'The blooming period occurs during late summer or early fall, lasting about 3-4 weeks.' iNaturalist, verifiable sightings within 25 km of DC annotated 'flowering': weeks 25 and 31 (one each). Forager Chef: after the flowers begin to branch out the tops are 'tougher and can be slightly unpleasant to chew.'

Where to look

Sunny woods edges, clearings, meadows and disturbed ground; logged most at Dyke Marsh, Huntley Meadows Park and along the Mount Vernon Trail, all look-only, and on the Sligo powerline meadow, which is Pepco land. No listed park allows picking leaves or flowers, so pick on private land with the owner’s permission.

Habitats
disturbed ground & waste places, vacant lots, old fields & meadows, woods edges, trailsides & thickets
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.

No picking here (5 places)
  • Dyke Marsh Wildlife Preserve

    10 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.

  • Huntley Meadows Park

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

    Look but don’t pick: Fairfax County parks ban removing any plant part without written permission.

  • Mount Vernon Trail

    5 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 Powerline Meadow (Pepco land)

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

    Pepco transmission-line land. Private property: pick only with the owner’s permission.

  • C&O Canal NHP (towpath, Georgetown to Great Falls MD and beyond)

    2 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.

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

  • tender tops snapped off before the flowers open and cooked like asparagus (Foraging Texas; Forager Chef)
  • blanched in lightly salted water until just tender, cooled, squeezed dry and used like cooked bitter greens (Forager Chef)
  • with bacon, tomato, chili and pecorino, or as Italian-style bitter greens with garlic and chili (Forager Chef)
  • harvest by bending the growing top to find where it is tender, like asparagus, and cut before the flower cluster branches out (Forager Chef)
  • soak very bitter cooked greens overnight in cold water to calm the flavor (Forager Chef)

Keeping

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

Use within
within a few days
Keeps fresh
About 2–3 days refrigerated in a perforated plastic bag, or wrapped in a damp paper towel inside one (general guidance for leafy greens; University of Maine).
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, cool, drain and package with 1/2-inch headspace. Frozen greens are for cooked dishes only. Greens are low-acid and may only be pressure-canned, never water-bath canned, so freezing is the practical home method.

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
native
Native range
throughout much of North America, except the far north
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
Patchy Estimate 84 = 69 research-grade iNaturalist sightings within 25 km + 140 needs-ID sightings counted at 10% (69 of the 685 research-grade Lactuca sightings here are Canada lettuce) + 1 'cultivated' (planted) sighting (rule A); that is tier 3 by count (rule B). Final tier 3.
Effort
Quick kitchen prep Snap off the tender tops where they bend easily, blanch them in salted water (or boil, discarding the first water) and cook them like asparagus or bitter greens.
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

36 sources, each linked to the original.

  1. List of Rare, Threatened, and Endangered Plants of Maryland (March 2026) Maryland Department of Natural Resources, Wildlife and Heritage ServiceBacks up: picking rules
  2. Rock Creek Park Superintendent’s Compendium National Park ServiceBacks up: picking rules
  3. 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
  4. Wild Lettuce (Lactuca canadensis) Illinois Wildflowers (John Hilty)Backs up: description, habitat, safety, season
  5. Wild Lettuce: Identification, Harvesting and Cooking (Alan Bergo, 2024, modified 2025; Wayback Machine copy) Forager ChefBacks up: description, uses, safety, season
  6. Wild Lettuce (Mark Vorderbruggen) Foraging TexasBacks up: description, uses, safety, season
  7. iNaturalist research-grade observations of Lactuca canadensis within 25 km of downtown DC iNaturalistBacks up: findability
  8. Lactuca canadensis L., Wild Lettuce (Digital Atlas of the Virginia Flora) Virginia Botanical Associates (Digital Atlas of the Virginia Flora)Backs up: habitat
  9. Lactuca canadensis L., tall lettuce Go Botany (Native Plant Trust)Backs up: habitat, safety
  10. Checklist of the Vascular Plants of the Washington-Baltimore Area (Shetler & Orli) Smithsonian National Museum of Natural HistoryBacks up: habitat, safety, picking rules
  11. Lactuca canadensis (Canada lettuce, wild lettuce) Lady Bird Johnson Wildflower CenterBacks up: habitat, safety, season, native or invasive status
  12. Bulletin #4180, Vegetables and Fruits for Health: Greens University of Maine Cooperative ExtensionBacks up: keeping
  13. Freezing Greens (Including Spinach) National Center for Home Food Preservation (University of Georgia)Backs up: keeping
  14. Got the Wintertime “Greens”? National Center for Home Food Preservation (University of Georgia)Backs up: keeping
  15. USDA PLANTS Database: Lactuca canadensis (LACA), native status USDA NRCSBacks up: native or invasive status
  16. Virginia Invasive Plant Species List (effective date: September 2024) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: native or invasive status
  17. 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
  18. 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
  19. 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
  20. Invasive Plants in the District DC Department of Energy & EnvironmentBacks up: native or invasive status
  21. Lettuce, Wild (Lactuca canadensis) (David G. Mills) Nature’s RestaurantBacks up: safety
  22. Wild lettuce (Lactuca virosa) toxicity (Besharat, Besharat & Jabbari, BMJ Case Reports, 2009) NIH National Library of Medicine (PubMed Central)Backs up: safety
  23. Sonchus asper (Prickly Sowthistle) NC State Extension Gardener Plant ToolboxBacks up: safety details
  24. Lactuca floridana (Florida Blue Lettuce) NC State Extension Gardener Plant ToolboxBacks up: safety details
  25. The Lettuce Labyrinth: Sorting Out Species (Green Deane) Eat The WeedsBacks up: safety details
  26. Lactuca canadensis, Wild lettuce (Illinois Plants database, ILPIN notes) Illinois Natural History Survey, University of IllinoisBacks up: safety, habitat
  27. Allergic contact dermatitis to lettuce (Anais Brasileiros de Dermatologia, 2025) NIH National Library of Medicine (PubMed Central)Backs up: safety, effort & ID risk, safety details
  28. Erechtites hieraciifolius (American Burnweed) NC State Extension Gardener Plant ToolboxBacks up: safety, effort & ID risk, safety details
  29. Erechtites (PROSEA, Plant Resources of South-East Asia) Pl@ntUse (PROSEA)Backs up: safety, effort & ID risk, safety details
  30. Pyrrolizidine Alkaloids: Biosynthesis, Biological Activities and Occurrence in Crop Plants (Molecules, 2019) NIH National Library of Medicine (PubMed Central)Backs up: safety, effort & ID risk, safety details
  31. Nebraska Plants Toxic to Livestock (EC3037, Stubbendieck et al., 2018): Prickly lettuce Nebraska Extension, University of Nebraska-LincolnBacks up: safety, safety details
  32. Lactuca canadensis, Canada Lettuce (Known Hazards) Plants For A FutureBacks up: safety, safety details
  33. Sonchus (Common Sowthistle) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  34. Lactuca biennis (Tall Blue Lettuce) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  35. iNaturalist verifiable observations of Lactuca canadensis within 25 km of Washington, DC, annotated 'flower budding', by week iNaturalistBacks up: season
  36. iNaturalist verifiable observations of Lactuca canadensis within 25 km of Washington, DC, annotated 'flowering', by week iNaturalistBacks up: season