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.