Willows are a very large and diverse group of trees.
More than 100 species grow in the United States and Canada, ranging in size from a few inches tall to trees as large as 4 feet in diameter. Black willow is the largest of the tree willows in Iowa, attaining heights of 30 to 60 feet and a diameter of 14 to 24 inches. It is native to all of Iowa except the far northwest corner. It often grows as leaning, multiple stem trees, although it can develop with single stems when growing under forested conditions. Its common associates in the floodplain woodlands include cottonwood, green ash, silver maple, boxelder, river birch and other moisture loving trees.