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(updated September 7, 2023) 

Tall Lettuce

Lactuca canadensis L.

Asteraceae (Aster Family)

▲ ▼  rosette stage

▲ ▼  rosette stage

▲   young plant starting upright growth

▲▼mature plants prior to flowering (tall lettuce on right above, prickly lettuce on left)

▲  stem leaves on mature plant

▲ top side of leaf

▲▼ undersides of leaf, showing hairs, but no spines/prickles along midvein

▲mature, flowering plant

 

 

Lactuca canadensis L., Tall Lettuce, Wild Lettuce: 

Bayer Code:  LACCA

US Code LACA

·         A winter/summer annual or biennial native to Missouri that is very similar to annual blue lettuce in growth habit, growing 5-10 feet tall with mostly unbranched stems (until flowering) that are hollow between the nodes

·         Stems are round, hollow, often yellow green with purple spotting

·         Basal leaves 10-12 inches long, about ¼ to 1/3 as wide, with moderate to deep lobes; lobes moderately toothed, margins sometimes with fine hairs; basal leaves end in a narrow lobe, not a broad triangular point as on Tall Blue Lettuce and Florida Lettuce

·         Upper stem leaves become increasingly smaller and more narrow; upper half of stem leaves usually unlobed

·         Leaves have soft hairs, not prickly appendages on midvein underneath, as with prickly lettuce

·         Inflorescence is an open panicle at the top of the stem with 50-100 individual heads; heads are about ¼ inch diameter, with about 10-25 ray florets per head; ray flowers are tiny, yellow to orange (sometimes with a reddish tip); petals may fade to bluish color with age

·         Involucre of bracts surrounding florets is urn-shaped, 8-10 mm long at start of flowering, lengthening to 10-14 mm long by fruiting

·         Flowers June-October

·         Fruit is small, oval, ridged achene, 3-4 mm long; numerous white hairs (pappus) 4-7 mm long are attached to a slender stalk at one end of the seed; stalk length is equal to or somewhat shorter than main fruit body

·         Leaves and stem have a tan to orange milky sap

·         Similar species:

     o   Hairy Lettuce, Downy Lettuce (Lactuca hirsuta) is very similar to tall lettuce, except L. hirsuta tends to have more hairs on leaves, and bract cluster (involucre) below individual heads is larger 13-20 mm at flowering/15-22 mm at maturity, compared to 8-10 mm long at flowering/10-14 mm long at maturity for L. canadensis

     o   Perennial Blue Lettuce. (Lactuca tatarica), non-native creeping perennial with creeping roots that grows only 2-3 feet tall, often in open colonies; inflorescences have larger, showy, blue florets; more common in northern Midwest

     o   Woodland Lettuce (Lactuca floridana), is quite similar to Tall Lettuce until flowering; wild lettuce has yellow ray flowers instead of blue to white, and tips of basal leaves end in a more triangular lobe; sap is also yellow, instead of white

     o   Willowleaf Lettuce (Lactuca saligna), a non-native species that appears similar to Prickly Lettuce, but has more linear to lanceolate, slightly lobed leaves with smooth margins, and only a few hairs, but no spines, along midvein on lower side of the leaf; leaves often more blue-green in color than other Lactuca spp.

     o   Prickly Lettuce (Lactuca serriola), a non-native species that can be readily identified by the row of stout hairs/prickles along midvein on lower side of the leaf and leaf margins, the lateral vertical orientation of stem leaves and yellow ray flowers; similar Willowleaf Lettuce has narrower leaves and no prickles along the lower leaf midvein

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