Populus sect. Aigeiros
|Populus sect. Aigeiros|
Populus section Aigeiros is a section of three species in the genus Populus, the poplars. Commonly known as cottonwoods, the species are native to North America, Aigeiros, 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 of P. deltoides.
They are large, deciduous trees 20–45 m tall, 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 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 that allow them to be blown long distances in the air before settling to ground.
Although each of the three cottonwood species has a different leaf pattern, they all have the same general diamond leaf shape.
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 in extreme 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 P. d. deltoides (Vermont south to northern Florida and west to about Michigan), the leaves are broad and triangular, 7–15 cm across at the base. Further west (Minnesota south to eastern Texas), the subspecies P. d. 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 West Texas, New Mexico, and Colorado, the subspecies P. d. 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 the eastern cottonwood, differing mainly in the leaves having fewer, larger serrations on the edge, and small differences in the flower and seed pod structure. Some consider P. fremontii to be a subspecies of P. deltoides.12
Populus nigra (black poplar), native to Europe and western Asia, is distinct in its much smaller leaves, 5–11 cm across, with a more rhombic (diamond) shape.
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 purposes where a cheap but strong enough wood is suitable. They are also widely grown as screens and shelterbelts. Many of the cottonwoods grown commercially are the hybrid 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.
- 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.
- Monster Ohio Cottowood - 528 points in 2005 on YouTube