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Published In: Species Plantarum 2: 796. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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1. Lactuca canadensis L. (wild lettuce)

Pl. 258 a, b; Map 1077

Plants annual or biennial. Latex light tan to pale orange. Stems (30–)100–200(–300) cm long, hollow between the nodes, glabrous or rarely pubescent with short, curled hairs, often purple-spotted. Leaves well developed along the stems, extremely variable; the basal and lower stem leaves mostly 20–30 cm long, sessile or more commonly with a winged petiole, narrowly ovate, ovate, or obovate in outline, variously toothed and/or deeply pinnately lobed, the margins minutely hairy, sometimes with a pair of narrowly triangular basal lobes clasping the stem, the undersurface with the midvein often short-hairy; the middle and upper stem leaves mostly linear to lanceolate, ovate, or obovate, pinnately lobed to nearly entire, the margins minutely hairy or rarely glabrous, the base narrowed or tapered, sometimes with a pair of narrowly to broadly triangular basal lobes clasping the stem, the undersurface glabrous. Inflorescences mostly well-branched panicles with 50–100 or more heads. Involucre cylindrical or urn-shaped, 8–10 mm long at flowering, elongating to 10–14 mm at fruiting, the bracts 17(–19). Florets (10–)17–22(–25). Corollas orangish yellow or orange (yellow elsewhere), occasionally reddish at the tip, sometimes turning blue with age or upon drying (rarely blue at flowering). Pappus 4–7 mm long. Fruits with the body 3–4 mm long, 1.5–2.0 mm wide, dark brown to black, flattened, with prominent lateral wings and a conspicuous ridge on each face, tapered abruptly to a slender beak somewhat shorter than to about as long as the body. 2n=34. July–September.

Common throughout the state (eastern U.S. west to North Dakota and Texas; Canada; introduced farther west in the U.S.). Bottomland forests, openings and margins of mesic upland forests, savannas, sand savannas, bottomland prairies, upland prairies, sand prairies, banks of streams and rivers, margins of ponds, lakes, and sinkhole ponds; also pastures, fallow fields, old fields, fencerows, railroads, roadsides, and open, disturbed areas.

Corolla color is a relatively easy way to separate L. canadensis from the vegetatively similar L. floridana, however, readers are cautioned that corollas of L. canadensis sometimes darken to blue upon withering or drying, and that a single plant in Scott County was observed during the present study in which a few of the heads were blue at flowering. Barkley (1986) noted that although corolla color is fairly uniformly orange in the western portion of the species’ natural range, to the east of St. Louis the color is bright yellow.

Numerous infraspecific taxa of L. canadensis have been described based on variations in leaf morphology and pubescence, including f. angustipes Wiegand, with entire or shallowly toothed, lanceolate to linear leaves; var. obovata Wiegand, with usually finely toothed, oblanceolate to narrowly obovate leaves, the base sagittate and clasping the stem; f. stenopoda Wiegand, with leaves similar to var. obovata, but the base tapered or narrowed and not clasping the stem; var. longifolia (Michx.) Farw., with the leaf lobes linear to narrowly triangular, the base sagittate and clasping the stem; f. angustata Wiegand, with leaves similar to var. longifolia but the base tapered or narrowed; var. latifolia Kuntze, with the leaf lobes broadly triangular to obovate, the base sagittate and clasping the stem; f. exauriculatata Wiegand, with leaves similar to f. latifolia but the bases tapered or narrowed; f. villicaulis Fernald, with leaves similar to f. latifolia but more or less hairy; and other varieties and forms. Whitaker (1944) studied interspecific hybridization in Lactuca and suggested that at least some of these variations were probably due to single-gene differences and are thus unworthy of formal taxonomic recognition.

Steyermark noted an earlier report of L. graminifolia Michx. from Butler County but excluded this species from the state’s flora based upon his redetermination of the historical specimen as L. canadensis. Lactuca graminifolia is a southern species (North Carolina to Arizona) with mostly basal, unlobed leaves that has usually blue corollas (as in L. floridana) but fruits resembling those of L. canadensis in their beaks and nervation. This specimen also is referred to L. canadensis in the present study.



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