Tall Blue Lettuce (Lactuca biennis)
“Tall” is just the word we were looking for to describe this plant, which grew to at least twelve feet (4 m) in a clearing in the woods in Beechview. It was blooming in the middle of September. This is indeed a close relative of the garden Lettuce (L.sativa). The generic name, an old Latin word from which the common name is derived, refers to the milky white sap.
Gray describes the genus and the species, which he lists as L. spicata:
LACTÙCA [Tourn.] L. LETTUCE. Heads several-many-flowered. Involucre cylindrical or in fruit conical; bracts imbricated in 2 or more sets of unequal lengths. Achenes contracted into a beak, which is dilated at the apex, bearing a copious and fugacious vегу soft capillary pappus, its bristles falling separately. — Leafy-stemmed herbs, with panicled heads; flowers of variable color, produced in summer and autumn. (The ancient name of the Lettuce, L. sativa L.; from lac, milk, in allusion to the milky juice.)
§ 3. MULGÈDIUM (Cass.) Gray. Achenes thickish, oblong, contracted into a short thick beak or neck; annual or biennial; flowers chiefly blue.
L. spicàta (Lam.) Hitchc. Nearly smooth biennial, tall (1-3.6 m. high), very leafy; leaves irregularly pinnatifid, sometimes runcinate, coarsely toothed, the upper cauline sessile and auriculate, sometimes clasping; heads in a large and dense compound panicle; flowers bluish to cream-color; achene short-beaked. (L. leucophoea Gray. ) — Low grounds, rather common.