| Populussect. Aigeiros | |
|---|---|
.jpg) | |
| Populus fremontii in fall color | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Malpighiales |
| Family: | Salicaceae |
| Genus: | Populus |
| Section: | Populus sect.Aigeiros Duby[1] |
| Type species | |
| Populus nigra L. | |
| Species | |
Populus sectionAigeiros is asection of three species in the genusPopulus, the poplars. Like some other species in the genusPopulus, they are commonly known ascottonwoods. The species are native to North America, Europe, and western Asia. In the past, as many as six species were recognized, but recent trends have been to accept just three species, treating the others as subspecies ofP. deltoides.
They are large, deciduous trees that are 15–30 m (50–100 ft) tall and diameters of 4 m (13 ft),[2] distinguished by thick, deeply fissured bark and triangular-based to diamond-shaped leaves that are green on both sides (without the whitish wax on the undersides) and without any obviousbalsam scent in spring. An important feature of the leaves is thepetiole, which is flattened sideways so that the leaves have a particular type of movement in the wind.
Male and female flowers are in separatecatkins, appearing before the leaves in spring. The seeds are borne on cottony structures that allow them to be blown long distances in the air before settling to ground.
The cottonwoods are exceptionally tolerant of flooding, erosion, and flood deposits filling around the trunk.
Although each of the three cottonwood species has a different leaf pattern, they all have the same general diamond leaf shape.
Eastern cottonwood (Populus deltoides) is one of the largest North Americanhardwood trees, although the wood is rather soft. It is ariparian zone tree. It occurs throughout the eastern United States, parts of southern Canada, and northern Mexico. Theleaves are alternate and simple, with coarsely toothed (crenate/serrate) edges, and subcordate at the base. The leaf shape is roughly triangular, hence the species name,deltoides. Their winter buds are enrobed in a protective, fragrant resin that coats young leaves when they unfurl from the bud.
In the typical subspeciesP. d. deltoides (Vermont south to northernFlorida and west to aboutMichigan), the leaves are broad and triangular, 7–15 cm across at the base. Further west (Minnesota south to easternTexas), the subspeciesP. d. monilifera (plains cottonwood; syn.P. sargentii) has somewhat narrower leaves, 5–10 cm wide at the base. This is also thestate tree ofNebraska,Wyoming, andKansas. In West Texas,New Mexico, andColorado, the subspeciesP. d. wislizeni (Rio Grande cottonwood; syn.P. wislizeni) occurs.
Fremont's cottonwood (P. fremontii) is native to the southwestern United States and western Mexico.[3] In the United States, the species can be found inArizona,California,Colorado,Idaho,Nevada,New Mexico,Texas, andUtah. In Mexico, it can be found in the states ofBaja California,Baja California Sur,Sonora,Chihuahua,Coahuila,Nuevo León,Mexico State, andPuebla.[4][5] It differs from the eastern cottonwood mainly in the leaves having fewer, larger serrations on the edge, and small differences in the flower and seed pod structure. Some taxonomists formerly consideredP. fremontii to be a subspecies ofP. deltoides.[6][7]
Black poplar (P. nigra) is native to Europe and Western Asia, is distinct in its much smaller leaves, 5–11 cm (2.0–4.3 in) across, with a more rhombic (diamond) shape.
Cottonwoods are widely grown fortimber production along wet river banks, where their exceptional growth rate provides a large crop of wood within just 10–30 years. The wood is coarse and of fairly low value, used for pallet boxes, shipping crates, and similar purposes where a cheap but strong enough wood is suitable. They are also widely grown as screens andshelterbelts. Many of the cottonwoods grown commercially are thehybrid of eastern cottonwood and black poplar,Populus × canadensis (hybrid black poplar or Carolina poplar).
Cottonwood bark is often a favorite medium for artisans. The bark, which is usually harvested in the fall after a tree's death, is generally very soft and easy to carve.
Cottonwood is one of the poorestwood fuels; it does not dry well, and rots quickly. It splits poorly, because it is very fibrous. It produces a low level of energy per unit of volume of wood.[8]
Cottonwoods serve as food for thecaterpillars of severalLepidoptera.