Tall Blue Lettuce
Lactuca
biennis
(Moench.) Fern.
Asteraceae (Sunflower Family)
(No photos yet)
Lactuca biennis (Moench.) Fern.,
Tall Blue Lettuce:
Bayer Code:
LACBI
US Code LABI
·
Very tall, unbranched (until flowering) winter/summer annual or biennial
U.S. native plant growing 2-8 feet tall; stems are smooth, green or tan
or purple-streaked and hollow between the nodes
·
Leaves at base of plant can be up to 12 inches long; leaves are deeply
lobed, with smaller teeth on lobes; terminal lobe is roughly triangular
in shape
·
Upper stem leaves become increasingly smaller and more narrow
·
Leaves usually hairless on top side, often with
short hairs on leaf underside midvein (not little spines, as with
Prickly Lettuce (Lactuca
serriola)
·
Inflorescence is an open panicle at the top of the stem; individual
heads are about ¼ inch diameter and have 15-30 disk florets with pale
blue to white petals
·
Involucre of bracts surrounding florets is urn-shaped, 7-12 mm long at
start of flowering, lengthening somewhat by fruiting; bracts of varying
lengths, often tapering to a purplish tip
·
Flowers July-October
·
Fruit is small, oval, ridged achene, 4-5 mm long; numerous white hairs (pappus)
4-6 mm long are attached to a slender stalk at one end of the seed;
stalk length less than ½ length of main fruit body
·
Leaves and stem have a milky-sap if broken
·
U.S. native more common north and east of Missouri; found in open woods,
roadsides; not usually a serious weed problem
·
Similar species:
o
Woodland
Lettuce, Tall Blue Lettuce, Florida Wild Lettuce (Lactuca
floridana), is very similar
to tall blue lettuce, but is a more southern-occurring species and can
only be definitively distinguished by the number of florets per head
inflorescence:
§
Lactuca floridana – has 10-15
florets per inflorescence
§
Lactuca biennis – has 15-30
florets per inflorescence
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
Wild Lettuce, Tall Lettuce (Lactuca
canadensis), is quite similar
to Tall Blue Lettuce until flowering; wild lettuce has yellow ray
flowers instead of blue to white, and tips of basal leaves end in long,
tapered point; 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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