Annuals or biennials, 25-150(-200+) cm. Leaves on proximal 2/3-3/4 of each stem; blades of undivided cauline leaves oblong, ovate, or elliptic, margins entire or denticulate, midribs sometimes sparsely pilose. Heads in (± pyramidal) paniculiform arrays. Involucres (8-)10-12+ mm. Phyllaries usually reflexed in fruit. Florets 10-15(-25+); corollas bluish or whitish, seldom deliquescent. Cypselae: bodies brown (often mottled), ± compressed-lanceoloid to -fusiform, 4-5 mm, beaks ± stout, 0.1-0.5(-1) mm, faces 5-6-nerved; pappi white, 4-5 mm. 2n = 34. Flowering (Jun-)Aug-Sep(-Oct). Moist to wet places, margins of thickets and woods; 10-200 m; Man., Ont.; Ala., Ark., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Mich., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis. The 'double' pappi of Lactuca floridana (and L. biennis) are very similar to pappi found in species assigned to Cicerbita Wallroth (ca. 35 spp., Europe, Asia, Africa). Return of the species to Cicerbita as C. floridana (Linnaeus) Wallroth may have merit.
From Flora of Indiana (1940) by Charles C. Deam
I have what I believe to be this species from the greater part of the state. It is frequent at least in the southern part and is usually found in woodland. It prefers shady woods along streams. Our manuals describe it as having the achene with a short, narrow beak. All of my specimens are beakless, at least none with a beak longer than 0.3 mm.
[Based upon leaf shape, Deam recognizes another species with white pappus called L. villosa. He observes that] this species is infrequent to frequent in the southern part of the state, becoming infrequent, local, or absent in the northern counties.
Robust, leafy-stemmed annual or biennial 5-20 dm; lvs mostly petiolate and not sagittate at the base, often hairy along the main veins beneath, otherwise glabrous or nearly so, the blade 8-30 נ2.5-20 cm, from elliptic (or cordate) and merely toothed to evidently pinnatifid; heads numerous in an ample, paniculiform infl, with 11-17(-27) blue (white) fls; invol 9-14 mm in fr; achenes 4-6 mm, narrowed upward, beakless or with a stout beak sometimes a third as long as the body, several-nerved on each face, tending to be thickened on the margins; pappus white; 2n=34. Thickets, woods, and moist, open places; N.Y. to Fla., w. to Minn., Kans., and Tex. June-Sept. (L. villosa, the form with merely toothed lvs)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.