Fremont Cottonwood (Populus fremontii)
Above: The old cottonwood at the Zig promontory, Hot Springs Canyon, May 1998
Below: These trees tend to form large-scale Cottonwood-Willow Gallery Forests along the San Pedro River, seen here along Cascabel Road at milepost 24, July 1, 2002:
Main sources: Petrides, George & Olivia Petrides, 1992, A Field Guide to Western Trees, pp. 174-76, Houghton-Mifflin; Zimmerman, Robert, 1969, Plant Ecology of an Arid Basin Tres Alamos-Redington Area Southeastern Arizona, Geological Survey Professional Paper 485-D, Washington, D.C.; see also the USDA Forest Service Database.
In dry country like ours, the presence of Cottonwoods unfailingly indicates presence of underground water near the surface. Below, on a promontory above the Upper Hot Springs Canyon streambed, one arm of a great tree rises out of view to the right, shading the whole area beneath it. But note especially the trunk of a fallen cottonwood giant lying behind the standing man -- a battered limbless portion, carried from a long ways upstream in a fairly recent flood (1993): (Click on the image for a closer view of the trunk.)
Below, an elder tree springs into fresh green at streamside in late February 2004. (Trunk and branches are darkened due to the recent rains. View is from a canyonside perch, far above the streambed.)
Cottonwoods share the genus Populus with the Poplars and Aspens -- trees whose leaves are mostly toothed and somewhat triangular, with 3-5 main veins meeting near the leaf base. They are all fast-growing and fairly short-lived species. young bark is smooth and greenish-white, old bark dark and thick, with deep furrows. At left, a view of young bark (tree is roughly 20 years old). Click on the images below to enlarge.
Fremont Cottonwood leaves are 2-5 inches long, broadly triangular, coarsely toothed, without glands, often with a tapering point and sometimes hairy beneath. Leaf stalks are long and flattened, and 3 to 5 main leaf veins meet near the leaf base. Cottonwood and its relative, the "Quaking Aspen", share the feature of a leaf stem which is flattened near the base (see left). The plane of flattening is perpendicular to the plane of the leaf, which permits the entire leaf to flutter with the slightest breeze (see Petrides, p. 174), creating the bright-shimmering effect that is so characteristic of both trees. (Functions of this unique pattern are not yet clearly understood.) (Click on the top two images at left to enlarge them.)
For more detailed images, Click here.