2. Helianthus annuus L. (common sunflower)
H. annuus var. lenticularis (Douglas)
Steyerm.
H. annuus var. macropocarpus (DC.)
Cockerell
Pl. 281 g, h;
Map 1189
Plants annual, with
taproots. Stems solitary, (25–)50–300 cm long, stout, moderately pubescent with
short, stiff, ascending, pustular-based hairs, these often breaking off toward
the stem base, leaving the persistent expanded base. Leaves well developed
along the stem (usually with 8–25 nodes), mostly alternate, long-petiolate.
Blades of the stem leaves 7–40 cm long, 3–35 cm wide, ovate to triangular-ovate
or broadly ovate-triangular (mostly 1.2–2.5 times as long as wide), flat or
sometimes slightly drooping, not folded longitudinally, cordate to truncate,
broadly rounded, or short-tapered at the base, tapered to a usually sharply
pointed tip, the margins finely to coarsely and often somewhat irregularly
toothed (rarely nearly entire), flat, the surfaces moderately to densely
roughened, pubescent with minute, loosely appressed, pustular-based hairs, also
with moderate to dense, sessile, yellow glands, more or less with 3 main veins,
the lateral pair branching from the midnerve at the base of the blade.
Inflorescences rarely of solitary terminal heads, more commonly appearing as
open panicles. Involucre 10–30 mm long, (15–)20–50 mm in diameter (longer and
much wider in cultivated forms), mostly shorter than or extending about to the
tips of the disc corollas, the bracts in 3 or 4 subequal to somewhat unequal
series, narrowly ovate to ovate, tapered to a sharply pointed, slender, loosely
ascending to more commonly spreading or recurved tip, the margins with
relatively long, stiff, spreading hairs, the outer surface moderately to
densely pubescent with short (or occasionally longer), stiff, loosely ascending
to spreading, pustular-based hairs, both surfaces also usually with small,
sessile, yellow glands. Receptacle flat or slightly convex, the chaffy bracts
9–12 mm long (slightly longer in cultivated forms), narrowly oblong-triangular,
usually 3-lobed above the midpoint, the lobes tapered to sharply pointed,
straw-colored to dark purple, inconspicuously short-hairy tips, the outer
surface usually glabrous below the tip. Ray florets 17–40 (more in cultivated
forms), the corolla 2.5–5.0 cm long, variously glabrous or both surfaces
inconspicuously hairy toward the base, or the outer surface minutely hairy and
occasionally also with minute, sessile, yellow glands. Disc florets with the
corolla 5–8 mm long, reddish brown to dark purple (at least the lobes and the
upper portion of the tube; rarely yellow elsewhere). Pappus of 2 scales 2.0–3.5
mm long, these narrowly lanceolate-triangular, tapered to a sharply pointed,
often minutely awnlike tip, papery, often also with 1–4 additional oblong
scales 0.2–1.0 mm long. Fruits 3–7 mm long (longer in cultivated forms),
narrowly wedge-shaped to obovate, flattened but usually more or less 4-angled
in cross-section, the surface glabrous or more commonly densely and minutely
hairy when young, but usually appearing glabrous or nearly so at maturity,
uniformly black to variously with gray, brown, or white stripes or mottling. 2n=34.
July–November.
Mostly absent
from the Ozark and Mississippi Lowlands Divisions but scattered elsewhere in
the state (nearly throughout the U.S.; Canada, Mexico). Upland prairies,
openings of bottomland to mesic upland forests, and banks of streams and
rivers; also crop fields, fallow fields, old fields, ditches, railroads, roadsides,
and open, disturbed areas.
The common
sunflower is the most important crop plant to have originated from a species
native to the United States. It is the state flower of Kansas, where sunflower
fields are a common sight. For a thorough account of this plant and its uses,
see Heiser’s (1976) enjoyable book on the genus. Helianthus annuus is
cultivated nearly worldwide for its edible seeds and for the oil produced from
the seeds, which is one of the most important of the world’s vegetable oils for
food production and also industrial and other uses. In recent years, the market
for sunflower seeds for wild bird feeding also has become increasingly
important in the United States. The species is cultivated as an ornamental, and
plants also are used to a limited extent for fodder for livestock and for
wildlife food plantings. At one time, Missouri was among the largest producers
of commercial sunflowers in the country, but production has shifted primarily
to other states, particularly North Dakota.
Heiser (1951,
1976) discussed the domestication of common sunflower. According to him, the
species originally was native to the western states. However, the remains of
fruits have been found by archaeologists in scattered prehistoric cliff
shelters as far east as South Carolina (including sites in Missouri). Heiser
noted that Native Americans had a long history of harvesting the plant from the
wild for food, oil, and a yellow dye, which led to its establishment as a weed
in and around sites of habitation and to its cultural dissemination among
tribes during pre-Columbian times. The plant became cultivated at some point,
which led to selection for traits such as fewer but larger heads and larger
fruits. As early as the 1500s, the species was brought to Europe by early
explorers and was cultivated there. It eventually became an important crop
plant in Russia, where the “mammoth Russian” type, with its unbranched stem,
greatly enlarged head, and large fruits, was bred. Cultivated forms of the
common sunflower subsequently were reimported into the United States as a crop
plant during the second half of the 1800s. Continued breeding both in Europe
and in this country have resulted in a large number of commercially available
cultivars adapted to different climates and for various uses. For example,
Steyermark (1963) recorded a few collections from Holt County and the city of
St. Louis of an ornamental dwarf form with the florets mostly converted to ray
florets, which has been referred to under the name cv. ‘Nanus Florepleno.’
Interestingly, the large-headed sunflower that was independently domesticated
by Native Americans survives in the American Southwest in a race known as the
Hopi sunflower, which is cultivated on a very limited basis in modern times.
The commercially important plants grown around the world today first originated
as a result of efforts by plant breeders in Europe.
Although at
times up to five taxonomic varieties of H. annuus have been recognized,
a formal infraspecific classification mostly has been abandoned, owing to
frequent hybridization that has blurred the boundaries between cultivated and
wild plants (Heiser et al., 1969). The original, wild plants of the
southwestern United States and adjacent Mexico at one time were called var. lenticularis
and differ in their more numerous, smaller heads with narrower (4–7 mm)
involucral bracts, smaller (2.0–3.5 cm in diameter) receptacles, fewer (17–26)
ray florets with shorter (2.5–4.0 cm) corollas, and small (3–5 mm) fruits.
Steyermark (1963) cited a single historical Missouri occurrence of this taxon
from Jackson County (but see below). At the other extreme, the commonly
cultivated plants (which rarely escape) were known in the past as var. macropocarpus
and have an unbranched stem with usually a solitary terminal head having big
(8.5–15.0 mm or more wide) involucral bracts, large (5.5–60.0 cm or more in
diameter) receptacles, more numerous (30–70) ray florets with longer (3.5–10.0
cm) corollas, and large (6.5–15.0 mm) fruits. The sunflower that is widely
distributed outside the original native range of the species has been called
var. annuus and is more or less intermediate between the other two main
variants for virtually every character. Heiser (1954, 1976) hypothesized that
this weedy variety either arose through introgressive hybridization between the
cultivated sunflower and the original wild type or that it evolved from the
so-called camp-follower weed that became established around prehistoric
habitations as an indirect result of harvesting of the species from the wild.
Given the
complex biogeographical and ethnobotanical situation surrounding the species,
it is not possible to address the issue of whether to consider the species
native in Missouri with any confidence. The oldest Missouri herbarium specimen of
common sunflower examined during the present study was collected in Cass County
by G. C. Broadhead in 1876 and represents the var. lenticularis phase
rather than the weedy phase. However, archaeological remains from digs at
prehistoric dwellings indicate that a probably cultivated variant was present
in Missouri hundreds or thousands of years ago (Heiser, 1978). Based on the
herbarium record, the weedy variant moved into the state relatively early,
reaching St. Louis County by 1896, Jasper County by 1905, and Marion County by
1914. It seems unlikely that H. annuus was ever a natural component of a
native plant community prior to European settlement of the state, but the
spread of the weedy variant into and across the state could be interpreted to
have occurred without any direct human assistance.
Heiser (1947)
studied natural and artificial hybridization between H. annuus and H.
petiolaris. He noted that the hybrids have reduced fertility but are not
totally sterile. Such hybrids have been reported from Cole and Jackson Counties
and the city of St. Louis and can be very difficult to distinguish
morphologically from one or the other parent.