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..
Perennial; stem 1 3/4°-3° tall, scabrous or hispid throughout. Leaves mainly on the lower part of the stem, very rough on both surfaces, ovate-elliptic to lanceolate, 21/2'-6' long, acute or acuminate at the apex, cu-neate or more abruptly contracted at the base, shallowly serrate or denticulate, the petioles of the lower cauline and basal leaves as long as the blades or longer; heads large, solitary or few, showy; rays several, yellow, 1 1/4'-1 1/2' long, drooping; bracts of the involucre linear, acuminate; disk ovoid or ovoid-globose, 2/3'-l' thick; chaff obtuse, canescent; pappus conspicuous, crenate or toothed.
Rudbeckia maxima Nutt. Trans. Am. Phil. Soc. (II) 7: 354. 1841.
Perennial; stem 3°-9° tall, simple or branched above, smooth, glaucous. Leaves oblong, oval, or ovate, or pandurate, 21/2'-8' long, mostly obtuse, undulate, repand-denticulate or entire, the upper sessile and partly clasping; heads large, showy; rays several, yellow, 7"-20" long; bracts of the involucres linear or linear-lanceolate, acute, short; disk cylindric to conic-cylindric, 1'-2 1/2' long; chaff abruptly short-pointed, pubescent at the summit; pappus conspicuous, denticulate, accentuated at the angles.
In moist soil, Missouri to Louisiana and Texas. June-Aug.
Rudbeckia laciniata L. Sp. Pl. 906. 1753.
Perennial; stem much branched, glabrous, or nearly so, 3°-12° high. Leaves rather thin, minutely pubescent on the margins and upper surface, broad, the basal and lower ones long-petioled, often 1° wide, pinnately 3-7-divided, the segments variously toothed and lobed; stem leaves shorter-petioled, 3-5-parted or divided, the uppermost much smaller, 3-lobed, dentate or entire; heads several or numerous, 21/2'-4' broad; rays 6-10, bright yellow, drooping; bracts of the involucre unequal; chaff of the receptacle truncate and canescent at the apex; disk greenish-yellow, at length oblong and twice as long as thick or longer; pappus a short crown.
In moist thickets, Quebec to Manitoba, Idaho, Colorado, Florida and Arizona. Thimble-weed. A double-flowered form in cultivation is called golden-glow. July-Sept.
A southern mountain race, lower, often only 1° high, with smaller heads, has been described as Rudbeckia laciniata humilis A. Gray.