Alder trees are a common sight in many landscapes, recognized for their adaptability and unique features. Understanding what an alder tree looks like can help in identifying them in various environments, from moist riverbanks to urban settings. This article will guide you through the distinctive visual characteristics of alder trees, focusing on their bark, overall shape, leaves, and reproductive structures.
Bark and Overall Form
Alder trees typically exhibit a conical shape when young, which can become more rounded or oval as they mature. Mature trees can reach heights of 28 meters (90 feet), with some species, like Red Alder, growing even taller, between 70 to 120 feet. While often single-stemmed, alder trees can also display a multi-stemmed growth habit.
The bark of young alder trees is generally smooth and olive-green, often featuring noticeable lenticels, which are small, horizontal lines or spots that aid in gas exchange. As the tree ages, the bark transitions to a darker greyish-brown color and develops shallow fissures, becoming rougher and sometimes forming cracked, square plates. Younger twigs can also be light brown with orange spots and may feel sticky to the touch.
Leaves, Catkins, and Cones
Alder leaves provide distinct identification clues. They are typically dark green, racquet-shaped, or broadly oval, and have a slightly leathery texture. The leaf tip is often rounded or indented, rather than pointed, and the margins are serrated or toothed. Young leaves can be shiny and sticky to the touch. The leaves are arranged alternately on the branches and generally remain green until they drop in the fall, turning brown rather than vibrant autumn colors.
Alder trees are monoecious, meaning they bear both male and female flowers on the same tree, appearing as catkins. Male catkins are long, pendulous, and cylindrical, measuring between 2 to 10 centimeters (1 to 4 inches), and turn yellow as they release pollen in early spring, before the leaves emerge. Female catkins are smaller, green, and oval-shaped, grouped in clusters of three to eight on each stalk.
After pollination, these female catkins develop into woody, cone-like structures. These small, brown “cones” are an identifying feature, measuring 1 to 2.5 centimeters (0.5 to 1 inch) long. They persist on the tree throughout the winter and into the following growing season. The seeds themselves are small, flat, and waxy, with thin, corky wings that allow them to float, aiding in water dispersal.