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 or biennial (rarely annual), mostly rigid, usually rough or hispid herbs, with alternate undivided lobed or pinnatifid leaves, and large long-peduncled heads of tubular (mostly purple) and radiate (yellow) flowers. Involucre hemispheric, its bracts imbricated in 2-4 series. Receptacle conic or convex, with chaffy concave scales subtending or enveloping the disk-flowers. Ray-flowers neutral, the rays entire or toothed. Disk-flowers perfect, fertile, their corollas 5-lobed. Anthers entire or minutely 2-mucronate at the base. Style-branches tipped with hirsute appendages. Achenes 4-angled, obtuse or truncate at the apex. Pappus coroniform, sometimes of 2-4 short teeth, or none. [In honor of Claus Rudbeck, 1630-1702, Swedish anatomist and botanist.]
About 30 species, natives of North America and Mexico. In addition to the following, some 20 others occur in the southern and western United States. Type species: Rudbeckia hirta L.
Disk globose or ovoid and purple or dark brown in fruit; lower leaves entire or lobed. Lower leaves deeply 3-lobed or 3-divided.
Plant more or less hirsute: leaves thin; chaff awned.
1. R. triloba.
Plant scabrous; leaves thick; chaff blunt, pubescent at apex.
2. R. subtomentosa.
Leaves neither 3-lobed nor 3-divided.
Plants hispid; style-branches subulate.
Stem leaves lanceolate to oblong; involucre shorter than the rays.
3. R. hiria.
Stem leaves oval to obovate; involucral bracts foliaceous, nearly as long as the rays.
4. R. Brittonii.
Plants pubescent or glabrate; style-branches obtuse. Chaff merely ciliate.
Leaves denticulate or entire; rays 9"-12" long. Basal leaves narrowed at base.
5. 7?. fulgida.
Basal leaves cordate at base.
6. R. umbrosa.
Leaves dentate or laciniate: rays about 18" loner.
7. R. speciosa.
8. R. grandiflora.
Disk elongated or cylindric in fruit, yellowish or gray. Leaves very thick, shallowly toothed.
9. R. maxima.
Leaves thin, pinnately divided or pinnatifid.
10. R. Iaciniata.
Rudbeckia triloba L. Sp. Pl. 907. 1753.
Stem somewhat pubescent and rough, rarely glabrate, branched, 2°-5° high. Leaves thin, rough on both sides, bright green, the basal and lower ones petioled, some or all of them 3-lobed or 3-parted, the lobes lanceolate or oblong, acuminate, sharply serrate; upper leaves ovate, ovate-lanceolate, or lanceolate, acuminate or acute, narrowed to a sessile base or into short margined petioles, serrate or entire, 2'- 4' long, 1/2'-1' wide; heads nearly 2' broad, corymbed; bracts of the involucre linear, acute; pubescent, soon reflexed; rays 8-12, yellow, or the base orange or brownish-purple; disk dark purple, ovoid, about 6" broad; chaff of the receptacle awn-pointed; pappus a minute crown.