This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual or biennial; stem glabrous, leafy up to the paniculate inflorescence, 2°-6° high. Leaves oblong, ovate or lanceolate, acuminate, acutely dentate or the teeth mucronate-tipped, glabrous above, pubescent with short stiff hairs on the veins beneath, sessile and slightly clasping at the base, or petioled, 4'-6' long, 1'-2 1/2' wide, the lowest sometimes lobed at the base; heads numerous, 3"-5" broad; peduncles usually minutely scaly; rays blue; involucre about 5" high, its outer bracts much shorter than the inner, some or all of them obtuse; achenes thick, oblong, little flattened, narrowed above; pappus white.
In thickets, New York to Illinois, Nebraska, south to Florida, Georgia and Kentucky. July-Sept. False lettuce.
Sonchus floridanus L. Sp. Pl. 794. 1753- Lactuca floridana Gaertn. Fruct. & Sem. 2: 362. 1791.
Mulgedium floridanum DC. Prodr. 7: 349. 1791.
Annual or biennial; stem glabrous, rather stout, leafy up to the large, paniculate inflorescence, 3°-7° high. Leaves deeply lyrate-pinnatifid, or sometimes cordate-ovate, sessile or petioled, 4'-12' long, glabrous above, pubescent on the veins beneath, the terminal segment usually broad, triangular, acute or acuminate, the lateral ones lanceolate to oval, acute, all usually dentate, or the leaves irregularly lobed; heads numerous, 3"-5" broad; peduncles commonly scaly; rays blue; involucre about 6" high, its outer bracts much smaller than the inner; achenes thick, somewhat compressed, narrowed above into a short beak; pappus white.
In moist, open places, southern New York and Pennsylvania to Illinois, Kansas, Florida and Texas. Porto Rico. July-Sept.
Sonchus spicatus Lam. Encycl. 3: 401. 1789. Mulgedium leucophaeum DC. Prodr. 7: 250. 1838. Lactuca leucophaea var. integrifolia A. Gray, Syn. Fl. 1: Part 2, 444. 1884. Lactuca spicata integrifolia Britton, Mem. Torr.
Annual or biennial; stem usually stout, glabrous, 3°-12° high, leafy up to the large, rather dense panicle. Leaves deeply pinnatifid or lobed to entire, sharply dentate with mu-cronate-pointed teeth, sessile, or the lower narrowed into margined petioles, glabrous on both sides, or pubescent on the veins beneath, 5'-12' long, 2'-6' wide; heads very numerous, about 2" broad; peduncles minutely scaly; rays blue to white; achenes oblong, compressed, narrowed above into a short neck; pappus brown.
In moist soil, Newfoundland to Manitoba, North Carolina, Tennessee, Iowa, South Dakota and Colorado. Ascends to 2000 ft. in North Carolina. Races differ in leaf-form and in color of the flowers. Milk-weed. July-Oct.