2. Populus deltoides W. Bartram ex Marshall (cottonwood, eastern cottonwood, southern cottonwood)
Pl. 553 h–k; Map
2568
Plants trees
15–35 m tall, relatively open, widely branched with mostly spreading to loosely
ascending branches. Bark light to dark brown, with a network of coarse,
longitudinal ridges and deep furrows. Twigs slender to more commonly stout,
yellowish brown to reddish brown, becoming tan or gray with age, glabrous or
sparsely pubescent with short, spreading to somewhat curved, white hairs, the
pith white. Winter buds 6–18 mm long, greenish yellow, strongly sticky with
yellowish resin, glabrous or sparsely spreading-hairy. Leaves somewhat
heterophyllous (the early-season leaves with fewer, deeper teeth than those
produced later), the petiole about as long as the blade, noticeably flattened
on the sides, at least near the tip, glabrous or hairy. Leaf blades 3–12(–14)
cm long, more or less triangular to broadly ovate-triangular, noticeably wider
than long to slightly longer than wide, broadest near the base, abruptly
tapered to a sharply pointed tip, truncate to broadly cordate at the base, the
margins minutely pubescent with moderate to dense, curved hairs, with a
well-defined, narrow, pale yellow or translucent line or band (viewed under
magnification), finely and unevenly scalloped or bluntly toothed, the teeth
mostly 5–20 and relatively coarse (early-season) or 20–50 finer (late-season)
per side, these 0.5–7.0 mm deep, incurved and minutely thickened at their tips,
sometimes also with 1–6 club-shaped gland(s) at or near the base, the upper and
undersurface grayish green to bright green, glabrous. Inflorescences 5–18 cm
long (the pistillate ones elongating to 10–24 cm at fruiting), the bracts
deeply cut into 9 to numerous irregular lobes, the margins glabrous, the
undersurface glabrous. Staminate flowers with mostly numerous (40 or more)
stamens. Pistillate flowers with 3 or 4 carpels, the style variously unbranched
nearly to the tip or branched nearly to the base, the stigmas flattened. Fruits
6–13 mm long, ovoid, glabrous, with 3 or 4 valves. 2n=38. March–May.
Scattered nearly
throughout the state, most abundant in counties bordering large rivers (nearly
throughout the U.S. except for some far-western states; Canada, Mexico).
Bottomland forests, banks of streams and rivers, margins of ponds and lakes,
sloughs, swamps, marshes, and bottomland prairies; also ditches, strip mines,
quarries, railroads, roadsides, and moist disturbed areas.
Cottonwood is a
fast-growing, large, stately tree that can attain massive trunk diameters. It
is cultivated as a shade tree and for erosion control and mine reclamation, but
is considered a relatively short-lived species.
Two hybrids that
are sometimes also planted in Missouri have been recorded as uncommon escapes
(Steyermark, 1963; Eckenwalder, 1977a). Carolina poplar, P. ×canadensis
Moench is a hybrid between P. deltoides and the nonnative P.
nigra. It is known thus far from historical collections from Iron and
Washington Counties. This hybrid has the more columnar growth form of its
Lombardy poplar parent and also has early-season leaves that are somewhat
longer than wide, with more numerous, finer teeth along the margins than in P.
deltoides. It is usually a staminate clone that reproduces vegetatively
from root sprouts. Balm-of-Gilead, P. ×jackii Sarg. (P. ×gileadensis
Rouleau) is a mostly sterile hybrid between the cultivated P. balsamifera
L. and P. deltoides. In Europe it is cultivated for its winter
bud resins. It usually occurs as a pistillate clone that reproduces
vegetatively from root sprouts. In Missouri, this hybrid is known thus far from
historical collections from Reynolds and St. Louis Counties. It differs from P.
deltoides in its petioles that are not or only slightly flattened laterally
and in its more narrowly ovate leaf blades with somewhat rounded bases.
Eckenwalder
(1977a, b) treated the P. deltoides complex as consisting of three
intergrading subspecies, two of which are found in Missouri. The third
subspecies, ssp. wislizeni (S. Watson) Eckenwalder (Rio Grande
cottonwood) occurs in the western United States and adjacent Mexico. It is most
similar to ssp. deltoides, differing from that subspecies in its leaf
blades mostly lacking basal glands and its sparsely hairy winter buds.