Populus sect. Aegiros
Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Malpighiales
Family:	Salicaceae
Genus:	Populus
Section:	P. sect. Aegiros
Species
Populus deltoides L. Populus fremontii Populus nigra L.

Populus section Aegiros is a section of three species in the genus Populus, the poplars. Commonly known as cottonwood, it contains three species native to North America, Europe and western Asia.

They are large deciduous trees 20–45 m tall, distinguished by thick, deeply fissured bark, and triangular-based to diamond-shaped leaves, green on both sides (without the whitish wax on the undersides of balsam poplar leaves), and without any obvious balsam scent in spring. An important feature of the leaves is the petiole which is flattened sideways, so that the leaves have a particular type of movement in the wind.

Male and female flowers are in separate catkins, appearing before the leaves in spring. The seeds are borne on cottony structures which 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.

Cottonwood trees' classification consists of 3 different species. Although each of these trees has a different leaf pattern, they all have the same general diamond leave shape. In the past up to five or six species were accepted, but recent trends have been to accept just three species, treating the others as subspecies of P. deltoides.

Populus deltoides (Eastern Cottonwood) is one of the largest North American hardwood trees, although the wood is rather soft. It is a riparian zone tree. It occurs throughout the eastern United States and just into southern Canada. The leaves 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.

In the typical subspecies deltoides (Vermont south to northern Florida and west to about Michigan), the leaves are broad triangular, 7–15 cm across at the base. Further west (Minnesota south to eastern Texas), the subspecies monilifera (Plains Cottonwood; syn. P. sargentii) has somewhat narrower leaves 5–10 cm wide at the base. This is also the state tree of Nebraska, Wyoming and Kansas. In western Texas, New Mexico and Colorado the subspecies wislizeni (Rio Grande Cottonwood; syn. P. wislizeni) occurs.

Populus fremontii (Fremont cottonwood) occurs in California east to Utah and Arizona and south into northwest Mexico; it is similar to Eastern Cottonwood, differing mainly in the leaves having fewer, larger serrations on the edge, and small differences in the flower and seed pod structure.

Populus nigra (Black Poplar), native of Europe and western Asia, is distinct in its much smaller leaves, 5–11 cm across, with a more rhombic (diamond) shape; see the link for further details.

[edit] Cultivation and uses

Cottonwoods are widely grown for timber 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, where a cheap but strong wood is suitable. They are also widely grown as screens and shelterbelts. Many of the cottonwoods grown commercially are the hybrid between Eastern Cottonwood and Black Poplar, Populus × canadensis (Hybrid Black Poplar or Carolina Poplar). In the West, a variant know as Hybrid Cottonwood are also grown.^[1]

Felling a cottonwood tree usually involves making an initial deep chainsaw cut to drain the water.^{[citation needed]}

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 poorest woods to use as wood fuel. It does not dry well, and rots quickly. It splits poorly, because it is very fibrous. It produces the lowest BTUs per cord of wood.^[2]

Cottonwoods serve as food for the caterpillars of several Lepidoptera (see list of Lepidoptera that feed on poplars).

[edit] References

This article uses bare URLs. Please help improve this article by turning bare URLs into proper citations containing all of the information on the referenced work's title, date, publisher, publication, and author, so that the article remains verifiable in the future. (There are several templates available that can help to make formatting such citations simple.) This page may also be able to help find problematic links. (November 2009)

[edit] External links

• Swamp Cottonwood, Populus heterophylla Large-format diagnostic photographs, species information. Morton Arboretum acc. 144-91-6
• Minnesota DNR big tree list The largest tree by circumference in Minnesota is a populus deltoides at 394 inches (1,001 centimeters) measured at the trunk 4 and 1/2 feet (137 cm) above the ground. This tree is 106 feet (32.31 meters) tall.
• Large Ohio Cottonwood Tree [1]