102. Senecio L. (groundsel)
Plants annual.
Stems erect or ascending, unbranched or few-branched, sometimes lined or
angled, glabrous or with patches of fine, woolly (cobwebby) hairs, sometimes
with scattered, minute hairs toward the tip. Leaves in a basal rosette and
alternate, progressively reduced in size from the stem base to tip,
cobwebby-hairy when young, often becoming glabrous or nearly so at maturity,
sessile or the lowermost long-tapered to a poorly defined petiole, the bases
strongly clasping the stem. Leaf blades sometimes pinnately lobed, the margins
otherwise shallowly or irregularly toothed or wavy to nearly entire, the
venation pinnate. Inflorescences terminal and axillary from the uppermost
leaves, panicles consisting of loose clusters to less commonly solitary flowers
at the branch tips, rounded to broadly rounded in profile. Heads discoid or
radiate, short- to long-stalked, with numerous florets. Involucre cylindrical
to slightly wedge-shaped, the bracts in 2 series, glabrous or nearly so, those
of the inner series more or less flat dorsally, those of the outer series
minute, ascending and usually incurved. Disc corollas bright yellow. Style
branches with a stigmatic line along each inner margin. Fruits narrowly oblong
to narrowly oblong-elliptic in outline, not flattened, 5–10-ribbed, minutely
hairy to less commonly nearly glabrous, brown. About 1,300 species, nearly
worldwide, but most diverse in the Old World.
The description
above applies only to the two species present in Missouri. Even in the
restricted sense, Senecio on a worldwide basis includes plants with a
bewildering array of growth forms and morphologies. Note that the native
Missouri species formerly classified in Senecio have been transferred to
the genus Packera.