The tall deciduous trees’ drooping flower clusters and brown woody strobiles (botanical name Alnus) are characteristics of alder trees. The two most prevalent alder tree species in North America and Europe are the Red Alder (Alnus rubra) and Black Alder (Alnus glutinosa), both of which are native.
Alders develop into towering shade trees or extensive shrubs in marshy, damp soil. The wide, rounded crown, serrated green leaves, and brown conifer-like cones of alders are easily recognized in landscapes. During the winter, the alder cones develop from catkins (conical flower clusters) and stay on the tree, giving the tree’s naked branches a distinguishing appearance.
In residential settings, alder trees are uncommon. They aren’t good trees for garden landscapes due to their enormous size, broad canopy, and fondness of damp locations. Nevertheless, alder hedge shrubs provide excellent privacy and security for certain smaller species.
This article covers everything you need to know about identifying the most prevalent alder trees in woodlands and parks. You’ll learn about the alder bark, leaves, flowers, and cones used to identify this majestic tree.
Alder Tree Facts
The genus Alders comprises of alder (Alnus) and other flowering deciduous trees that flourish in damp environments. Large trees and shrub-like trees make up around 35 alder species. Alder trees grow to a height of 66 to 100 feet (20 to 30 meters). The majority of alder species grow in USDA zones 5 through 8, although certain individuals may be more or less frost-tolerant.
Alders, which live between 60 and 70 years on average, are generally fast-growing trees. Yet, alder trees have been known to live up to 100 years. The alder species has a unique characteristic in that it thrives on damp, wet soil. Rivers, stream banks, marshy land, and wetlands are all home to alders. Alders are well-liked for re-foresting land with poor soil or drainage since this is a reality.
The bent, twisted branches of an alder tree create an arching, conical crown. The lustrous green pointed ovate or rounded leaves that arch over the branches are mostly serrated along the margins, and they are shiny green. The bark on branches is light gray to dark gray, much like the trunk. Birch trees (Betula) are cousins of alder trees. The cones of alders and birches are different. During the fall, alder female flowers develop into woody conical cones.
Alder Tree Leaves
The individual species can be identified by examining the serrated edge of alder leaves. From the midriff to the serrated leaf edge, alder tree leaves have egg-shaped blades with a central vein and parallel veins. Some have serrated edges and pointed tips, while others are smooth and rounded.
The red alder (Alnus rubra), green alder (Alnus alnobetula), and white alder (Alnus rhombifolia) all have similar leaves. The petiole of the ovate-shaped leaves is broader, with serrated margins. The alder leaves of white are more rounded than pointed, though.
The broader end of black alder leaves is opposed to the stem, and they are wedge-shaped. Alder trees lose their leaves in the autumn, making them a kind of deciduous tree. Most alder species have leaves that aren’t particularly colorful when they fall. When they’re still green, many drop their leaves. In the fall, the leaves of the red alder turn yellowish-brown.
Alder Tree Flowers
Male alder tree flowers (catkins) are long and slender, whereas female alder tree flowers (strobiles) become woody spherical cones. Monoecious trees, also known as alders, have male and female flowers on the same tree. The distinctive stiff, woody cones that alder trees are recognized for develop from the female blooms.
Early in the season, alder trees flower, and even in late winter. The dangling male flowers that bloom first are a distinguishing characteristic of an alder tree. Later, at the end of branches, smaller female catkins grow upright. The female blossoms stay on the tree until the strobiles, which are hard cones, fall in autumn.
Male alder flowers are tall, drooping clusters that may grow to 6 inches (15 cm) long. The furry feel to the pendulous catkins makes them soft and limp. On exposed branches, alder flowers develop and bloom. The pale gray, practically white bark and branches contrast with the colorful reddish-brown or yellow-brown catkins.
Male alder flowers (catkins) in closeup.
Alder Tree Cones
The most prominent feature of alder trees is their alder cones. Alder cones have a rounded, conical, or barrel-like shape and are up to 1″ (2.5 cm) long. In late fall and winter landscapes, the little, pine-like hard cones (strobiles) dangling from the end of bare alder branches help identify alder trees.
On the tree until the following spring are the hard brown alder strobiles (strobiles). As with many conifer tree cones, alder cones have seeds. The alder tree species, on the other hand, is an angiosperm, or flowering plant, which is important to remember. Conifer-bearing gymnosperms, such as pine trees and conifers, are the polar opposite.
Alder Tree Bark
The smooth, ash-gray to white color of ivy climbing on alder tree trunks is similar to that of some birch trees. The bark of ashen trees may darken as they age. Alder tree trunks are commonly covered in white lichen and moss, which is another way to identify this big tree.
Lichen and moss adorn the red alder tree bark, which has light gray bark with reddish-orange inner bark.
Hardwood trees include alder wood. Because of its relative softness, alder timber is incredibly workable. Unlike walnut, ash, or maple wood, alder wood isn’t as robust. Softwoods like pine and poplar tree wood are only slightly harder than alder. The rich, light color and straight grain patterns of alder wood are its appealing qualities. Alder wood is a semi-hardwood that is ideal for furniture, cabinets, musical instruments, and wooden household items because of its durability.
Alder Tree Identification
The brown hard, cone-like strobiles that dangle from bare brown-purple twigs with orange markings are easily recognized as alder trees. The light gray bark and orange-brown drooping blooms of alder trees are also visible. The pointed egg-shaped green leaves with serrated edges are another identifying feature of alder trees.
Types of Alder Trees with Pictures and Names
Let’s take a closer look at some of the most common alder tree varieties. In landscapes, descriptions and images of alder tree cones, leaves, and bark may be used to identify them.
Red Alder (Alnus rubra)
The red alder (Alnus rubra) tree is a big deciduous tree with tiny oval, brown wood cones, ovate leaves, and mottled light gray smooth bark. It has small oval, brown wood cones and mottled light gray smooth bark. With a slender, rounded crown, its spreading branches create a conical shape.
Between 66 and 100 feet (20 and 30 meters) tall, red alder trees grow. The genus Alnus contains the largest red alder tree. The dangling flower clusters are an simple way to identify alder trees, as they are with other alders. In the spring, long cigar-shaped blooms hang down. Female catkins develop into stiff, brown seed cones that produce red alder fruit.
The most common way to identify this tree species is by looking for red alder cones and catkins. The alder cones are dry conical and rounded, measuring 0.8″ to 1.2″ (2 cm). When the seeds are dispersed in winter, the hard, dark-colored cones on the tree persist.
The leaves of red alder trees are used to separate them from white alder (Alnus rhombifolia). White alders have double-serrated or finely serrated margins on their leaves, which are yellowish-green. In addition, the leaves’ margins on red alder have revolute edges, which feature rolled teeth.
Red alder trees, which are native to the west coast of North America, grow well in USDA zones 5 through 9. On the banks of rivers and streams, as well as in wetlands, you may see red alders. In full sun and wet, unproductive soil, red alder trees flourish best. The ruggedness and attractive appearance of red alder wood make it a favorite hardwood for furniture manufacture.
The red inner bark of the alder tree (left) and the outer red bark (right) When the smooth ash-gray bark is scraped or bruises, it becomes rusted red. The moss or lichen that grows on exposed branches may also be used to identify red alders in the landscape.
A dull green, ovate shaped, and alternately arranged red alder leaf is found on grayish branches. The leaves are 2.7–5″ (7–13 cm) long and have serrated, rough edges. The revolute toothed serration along the edges is an identifying characteristic of red alder leaves.
Black Alder (Alnus glutinosa)
The black alder (Alnus glutinosa) is a tall, medium-sized deciduous tree with rounded glossy green leaves and dark-brown hard conifer-like cones. Immature trees have greenish-brown black alder bark that becomes dark gray and scaly as they age. Between 40 and 60 feet (12 and 18 meters) tall and broad, black alders may be found.
Black alder trees are distinguished by their simple obovate leaves. These common alder leaves are distinguished from other types of alder trees by their wide, rounded end. Little woody black alder cones, like those seen in all alder species, help identify trees in winter settings.
Alder blooms are pendulous cylindrical clusters of redish flowers that range from 2 to 4 inches (5 to 10 cm) in length. Smaller than the tall long male blooms, the short green female blooms are tiny. Female black alder blooms on the tips of branches and has only up to 1″ (2.5 cm) long flowers.
The typical black cones that form from female catkins are known as black alder fruit. The black or coppery-brown alder cones are up to 1 inch (2.5 cm) long. The dangling clusters of blackish cones are recognizable. The common alder, European alder, or European black alder are all names for the same tree species found throughout Europe.
The tree’s botanical name, Alnus glutinosa, alludes to the sticky, resin-like substance that collects on purple-brown buds and young leaves. The lack of lower branches on big trees distinguishes black alders from other alders as a growth characteristic. As a result, European alders aren’t ideal shade trees.
Egg-shaped, obovate leaves with a broad rounded end that narrows to the stem, black alder leaves are alder leaves. 5″ (13 cm) long and broad, the leaves are up to 4″ (10 cm) long and broad. The glossy green leaves have a fuzzy appearance to them. In the autumn, leaves fall from the tree without changing color, wither, and die.
White Alder (Alnus rhombifolia)
White alder (Alnus rhombifolia) is a medium-sized, quick-growing tree with pale gray bark, diamond-shaped, round glossy green leaves, and yellowish catkins. thrive in wet, marshy ground in woodlands and forests, growing between 50 and 80 feet (15 to 24 meters) tall. White alder bark has smooth, even surfaces that get progressively darker with deep fissures. mature trees has a reddish tone, similar to that of the related red alder tree.
After the female catkins have bloomed, white alder fruit develop as hard, barrel-shaped dark cones. The woody cylindrical cones can grow up to 1.5 cm (0.6 in) long.
The white alder (Alnus rhombifolia) uses the term “alder catkin” to describe its leaf form. The serrated edges of the leaves create an diamond-shaped whole. The serrated revolute margins of white alder leaves differ from those of red alder tree leaves.
White alder leaves have an elliptic to rhomboid form with double serrated margins and a dark green glossy sheen. They have an elliptic to rhomboid form. Between 2.3 and 4 inches (6 and 10 cm) long and up to 2 inches (5 cm) broad, each white alder leaf grows.
Speckled Alder or Grey Alder (Alnus incana)
The alder speckled (Alnus incana) is a big shrub or medium-sized tree that grows in grey and brown tones. Dull, rounded green leaves, dangling spring blooms, and tiny stiff cylindrical cones characterize the grey or speckled alder. USDA zones 3 – 6 are ideal for this deciduous alder tree.
The speckled alder stands at around 8 feet (2.4 meters) tall as a multi-stemmed, shrubby plant. In wet ground, you may also grow the speckled alder as a small landscaping tree. The alder tree, which grows between 15 and 25 feet (4.5 and 7.5 meters) tall in full sun or partial shade, is a fast-growing tree.
The clusters of hard, black seeds on gray alder bark distinguish it from speckled alder. Green ovoid cylinders become dark brown as they mature into alder cone-like structures. Dangling male flowers with a yellowish color grow alongside the speckled alder cones.
Grey alder tree leaves are ovate, wedged-shaped with rough teeth along the margins and appear as gray alder cones and catkins. Between 2″ and 4″ (5–10 cm) long and up to 2″ (5 cm) broad, the matte green alder leaves grow.
Green Alder (Alnus alnobetula)
Green alder (Alnus alnobetula) is a large fuzzy green ovate to spherical leafed shrub with serrated edges that has distinctive uneven serration along the margins. ushes may reach 32 feet (10 meters) in height, although they are more likely to be 3 to 10 feet (1 to 3 meters).
The green alder is a good hedge plant because the many stems develop in clusters. Green alder cones form loose clusters and grow up to 0.6″ (1.5 cm) long with an oval shape. In the spring, green alder branches bloom with foliage and produce flowers. Male catkins, like all alder catkins, are long and slender dangling flower clusters. The alder cones, which are characteristic of female alder flowers, develop from the end of twigs.
The green alder tree is sometimes known as Alnus viridis, which is the scientific name for it. Most botanists, however, believe that the botanical name Alnus alnobetula is incorrect and should be used instead.
Alder leaves have a rounded, oval form and a smooth, green surface. They have a rounded, oval form. 3″ (7.5 cm) broad and long alder blades develop. The leaf edges are sharply serrated, giving the leaves a jagged appearance, as seen in other alder leaves.
Hazel Alder or Tag Alder (Alnus serrulata)
Hazel Alder is a multi-stemmed tiny shrub or medium-sized tree with smooth gray bark, brownish-yellow male blooms, and bright red female blooms, dull green leaves, and 1-inch (2.5-cm) long strobiles. USDA zones 4 to 9, full sun, and wet, soggy soil are ideal for the hazel alder.
Hazel trees grow to be 10 to 15 feet (3 to 4.5 meters) tall and broad, with a diameter of up to 15 feet (4.5 meters). The heavily serrated leaf edges are referred to by the botanical name Alnus serrulata. Tag alder and smooth alder are two other names for this tree.
Hazel alder catkins are brownish nut-like cones that grow up to 1″ (2.5 cm) long and have dark copper-colored nuts. The winged nutlets in the woody alder fruits resemble tiny pine cones.
Green, ovate, or elliptical blades with serrated margins make up the leaves of Hazel alder. The leaves are 1″ to 3″ (2.5 to 7.5 cm) long and relatively small, smooth, and dull green. Hazel alder leaves may be identified by their pointed tips and wedge-shaped base.
Seaside Alder (Alnus maritima)
Male catkins and seaside alder (Alnus maritima) leaves The dark, glossy green oval leaves with a wedge-shaped base and serrated edges make up the seaside alder. Female conical flowers develop into egg-shaped cones, as do those of other alder species. Alnus maritima grows in coastal and marine environments, as its common name suggests.