67. Coreopsis L. (tickseed, coreopsis)
(Smith, 1976)
Plants annual or
perennial herbs (shrubs elsewhere). Stems erect or ascending, unbranched or
more commonly few- to numerous-branched, with several fine to coarse longitudinal
lines or ridges, sometimes relatively strongly 4- or 5-angled, glabrous or
sparsely to moderately pubescent. Leaves opposite and sometimes also basal,
variously sessile to long-petiolate, the bases slightly expanded and wrapping
around the stem. Leaf blades simple or 1 or 2 times pinnately or less commonly
palmately lobed, dissected, or compound, variously shaped, the margins
otherwise entire, glabrous or variously hairy, not glandular. Inflorescences of
solitary terminal heads or appearing as loose, open clusters or panicles, the
heads with long, bractless stalks or the stalk with 1 or 2 inconspicuous,
minute bracts. Heads radiate. Involucre cup-shaped, the bracts in 2 dissimilar
overlapping series. Involucral bracts fused at the base, those of the outer
series (5–)8(–12), shorter and narrower than the others, ovate-triangular to
narrowly triangular, tapered to the sharply pointed tip, green, sometimes
reddish-tinged, the margins sometimes thin and white, often with spreading
hairs, the surfaces glabrous (the outer surface sometimes sparsely to
moderately hairy in C. tripteris), not glandular, usually
inconspicuously 3-nerved; those of the inner series usually 8, oblong-elliptic
to oblong-ovate, rounded or angled to a bluntly or less commonly sharply
pointed tip, yellowish brown to yellowish green, sometimes reddish-tinged, more
or less scalelike with usually broad, lighter, thinner margins, glabrous, not
glandular, inconspicuously several-nerved. Receptacle flat or slightly convex,
not elongating as the fruits mature, with chaffy bracts subtending the disc
florets, these variously shaped, relatively flat, not or only slightly wrapped
around the florets. Ray florets (5–)8, sterile (lacking stamens and style at
flowering and with an ovary that is shorter and thinner than those of the disc
florets, not developing into a fruit; pistillate elsewhere), the corolla showy,
12–30 mm long, relatively broad, yellow, or occasionally orangish yellow
(usually with a reddish brown to brownish purple base in C. tinctoria),
not persistent at fruiting. Disc florets 40–80(–150), perfect, the corolla
yellow to orangish yellow or reddish purple, not thickened at the base, not
persistent at fruiting. Style branches with the sterile tip slightly to
moderately elongate and tapered to a bluntly or sharply pointed tip. Pappus of
the disc florets of (1)2 short awn(s) (these smooth or with sparse,
upward-angled barbs), sometimes reduced to a low rim or crown with 1 or 2 short
teeth or absent, when present usually persistent at fruiting. Fruits 2–7 mm
long, narrowly oblong to oblong-ovate or oblong-obovate in outline, strongly
flattened, flat or more commonly the base and tip appearing curled or arched
inward at maturity, more or less truncate at the tip, not beaked, the angles
usually with slender to broad wings, the surfaces relatively flat to slightly
convex and with a faint longitudinal angle, the inner face sometimes with a
bulbous thickening at 1 or both ends, glabrous, sometimes appearing finely
pebbled or with numerous small tubercles, dark brown to black with pale wings,
often slightly shiny. About 140 species (depending on the generic
circumscription), mainly North America, but also Central America, South
America, Africa, Pacific Islands.
Several species
of Coreopsis are cultivated as garden ornamentals and for cut flowers,
and doubled cultivars with numerous ray florets have been developed for some of
these species. The fruits also provide food for birds and small mammals. Some
authors have noted that the genera Bidens and Coreopsis are
difficult to separate morphologically (Sherff, 1955; Barkley, 1986). Recent
molecular phylogenetic studies (Kimball and Crawford, 2004) also found that, as
traditionally circumscribed, the two genera are not natural units. Further
research undoubtedly will result in the revision of generic circumscriptions in
the subtribe Coreopsidinae.