5. Lactuca saligna L. (willow-leaved lettuce)
Pl. 259 a, b;
Map 1081
Plants annual or
biennial. Latex white. Stems (30–)50–100 cm long, hollow or more commonly solid
between the nodes, glabrous, whitish tan. Leaves well developed along the
stems, 2–15(–20) cm long, sessile or occasionally appearing as having a winged
petiole, linear and unlobed or narrowly elliptic-lanceolate in outline and with
1 or 2 pairs of linear lobes, the margins otherwise entire, glabrous, all or
mostly with a pair of narrowly triangular basal lobes clasping the stem, the
surfaces glabrous or the undersurface rarely sparsely short-hairy along the midvein.
Inflorescences spikelike panicles with 30–100 or more heads. Involucre
cylindrical, 7–9 mm long at flowering, elongating to 10–15(–18) mm at fruiting,
the bracts 17(–19). Florets (9–)11–14(–16). Pappus 4–6 mm long. Corollas light
yellow to yellow, sometimes some of them bluish- or purplish-tinged on the
undersurface. Fruits with the body 3.0–3.5 mm long, about 1.0–1.5 mm wide,
greenish brown to dark gray, flattened, with 5–7 conspicuous nerves or ridges
on each face, tapered abruptly to a slender beak 1.5–2.0 times as long as the
body. 2n=18. July–October.
Introduced,
scattered nearly throughout the state, but less common or absent from the Ozark
Border and Mississippi Lowlands Divisions and the eastern half of the Ozarks (native
of Europe, Asia; introduced widely in the U.S., Canada). Banks of streams and
spring branches, margins and openings of bottomland forests, margins of glades,
and disturbed portions of bottomland prairies; also banks of ditches, levees,
fallow fields, gardens, pastures, railroads, roadsides, and open, disturbed
areas.
This species is
relatively distinctive in its narrow leaves and spikelike inflorescences. Two
major infraspecific taxa based on leaf morphology have been recognized by some
authors, but the application of these names to the plants was confused by
Steyermark (1963) and in some of the earlier floristic literature. Plants with
unlobed leaves represent the typical form of the species (var. saligna).
Steyermark (1963) called plants with mostly pinnately lobed leaves f. ruppiana
(Wallr.) Beck., but that name also refers to entire-leaved plants. F. ruppiana
is by far the more common phase in Missouri. Plants with divided leaves are
more properly referred to as var. runcinata Gren. & Godr. (Feráková,
1977; Yatskievych and Turner 1990). However, Barkley (1986) noted that plants
with all entire leaves, those with all divided leaves, and intermediates can
occur in the same population, and these variants thus are not treated further
in the present study.