Alders are trees that compose the genus Alnus in the birch family Betulaceae. The genus includes about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few species extending into Central America, as well as the northern and southern Andes.
Alders can be trees or large shrubs. Depending on the species, they can grow from small, multi-stemmed shrubs to tall trees up to 35 meters in height. The leaves of alder trees are usually simple, alternate, and can range from broadly ovate to elliptical. They often have serrated or double-serrated edges. Some species have leaves with a distinctive shape, like the deeply lobed leaves of certain cultivars. The color is typically a vibrant green, though some species or varieties might show variations like greyish or bluish hues beneath.
Young alders have smooth bark, often with a grey or greenish color. As they age, the bark can become more textured, fissured, or even scaly. Some species have bark that’s used for natural dyes.
Alders are monoecious, they have both male and female flowers on the same tree. Male catkins are long, pendulous, and appear in clusters. Female catkins are smaller, upright when pollinating, and develop into woody cones that contain seeds. After pollination, female catkins develop into small, woody, cone-like structures that persist on the tree, often through winter. These cones release tiny winged seeds.
Many alder species are deciduous, losing their leaves in autumn. Before falling, leaves might turn a yellowish color, though this isn’t always particularly vibrant. Alder species thrive in wet soils and are often found along riverbanks, in wetlands, or in floodplains. They can tolerate flooding and help stabilize riverbanks.
Alder Trees
Common Alder (Alnus glutinosa)
The Common Alder is identified by its rounded, notched leaves that appear as though the tip has been pinched off, dark green and slightly sticky when young — a trait behind its species name glutinosa, meaning “sticky.” Its bark is dark grey-brown and fissured with age, and its small, woody, cone-like catkins persist on the branches through winter, making it easy to identify even without leaves.
Native to Europe, southwestern Asia, and North Africa, it is most commonly found growing in wet, waterlogged soils along riverbanks, streams, marshes, and lakesides, where few other large trees can thrive.
Red Alder (Alnus rubra)
The Red Alder is the largest alder in North America and can be identified by its thin, smooth, whitish-gray bark — which reveals a striking reddish-orange inner bark when scratched or cut, giving the tree its common name. Its leaves are oval to elliptical with slightly rolled-under margins and coarsely toothed edges, dark green above and paler beneath.
It is native to the Pacific Coast of North America, ranging from Alaska south through British Columbia, Washington, Oregon, and into northern California, where it thrives in moist lowland forests, floodplains, and disturbed areas.
White Alder (Alnus rhombifolia)
The White Alder takes its name from its pale, whitish-gray bark, which is smooth in younger trees and becomes irregularly furrowed and plated as it matures. Its leaves are distinctively diamond- to oval-shaped (rhomboid), finely double-toothed, dull green on top, and yellowish-green beneath with fine hairs along the veins. It can also be identified by its drooping male catkins that appear in late winter before the leaves emerge.
Native to the western United States, it is found along stream banks and river corridors from Idaho and Montana south through California and into Baja California, Mexico.
Speckled Alder (Alnus incana subsp. rugosa)
The Speckled Alder is most readily identified by its distinctive bark, which is dark reddish-brown to grayish and covered with conspicuous pale, horizontal lenticels that give it the characteristic “speckled” appearance for which it is named. Its leaves are broadly oval to elliptical, doubly serrated, dark green above, and pale and slightly downy beneath.
It typically grows as a large shrub or small multi-stemmed tree rather than a single-trunked specimen. Native to northeastern North America, it is commonly found in wetlands, bogs, streamsides, and wet thickets from Canada down through the northeastern United States.
Sitka Alder (Alnus viridis subsp. sinuata)
The Sitka Alder, also known as the Slide Alder or Wavy-leaf Alder, is identified by its sharply and irregularly toothed, ovate leaves that have a slightly wavy or sinuate margin — a feature embedded in its subspecies name. The bark is smooth and grayish-green to brownish, and the tree often grows in sprawling, multi-stemmed thickets rather than as a single upright trunk.
Its flexible, arching stems are another key identifier. It is native to the coastal and montane regions of Alaska, western Canada, and the Pacific Northwest of the United States, where it is most commonly found in avalanche chutes, subalpine meadow edges, and along mountain streams.
Arizona Alder (Alnus oblongifolia)
The Arizona Alder is identified by its elongated, oblong to oval leaves — a feature reflected in its species name oblongifolia — with sharply double-toothed margins, a dark glossy green on the upper surface, and a paler, slightly hairy underside. Its bark is smooth and gray-brown when young, becoming more furrowed and scaly with age.
It typically grows as a medium-sized tree in canyon bottoms and along permanent streams. It is native to the riparian zones of the American Southwest, particularly Arizona and New Mexico, and extends southward into the Sierra Madre Occidental of northwestern Mexico, where it is one of the few alders adapted to drier, high-elevation desert mountain environments.
Italian Alder (Alnus cordata)
The Italian Alder is one of the easiest alders to identify due to its distinctively heart-shaped (cordate) leaves, which are glossy, deep green on the upper surface with a pointed tip and finely toothed margins. It produces unusually large, cone-like fruiting catkins — among the largest in the genus — which persist on the branches and are a reliable identification feature year-round.
Its bark is gray and relatively smooth. Native to southern Italy and the island of Corsica, it has been widely planted as an ornamental and street tree across Europe and temperate regions of the world, valued for its tolerance of dry and alkaline soils, which is uncommon among alders.
Gray Alder (Alnus incana)
The Gray Alder is identified by its dull, grayish-green leaves, which are oval to elliptical, pointed at the tip, doubly toothed, and noticeably gray and downy — almost felted — on the underside, which gives both the tree and its species name their grey character. Unlike many alders, its leaves are not sticky when young.
The bark is smooth and pale gray, remaining relatively uncracked even on older trees. Native across a broad range from Europe to Siberia and Central Asia, it grows in cold, mountainous regions, along river banks, and in wet woodlands, and is widely used in land reclamation and afforestation due to its hardiness in poor, cold soils.
Green Alder (Alnus viridis)
The Green Alder is identified by its bright, vivid green leaves — the greenest of all the alders, as its name suggests — which are ovate, sharply and doubly toothed, and glossy on both surfaces with little to no hair. Unlike many alders, its male catkins develop in spring alongside the leaves rather than hanging in winter, which is a helpful identification clue.
It typically grows as a multi-stemmed, sprawling shrub rather than a tall tree. It is found across the mountains of central Europe, Russia, Scandinavia, and parts of North America, colonizing rocky, alpine, and subalpine slopes, avalanche paths, and stream margins at high elevations.
Himalayan Alder (Alnus nepalensis)
The Himalayan Alder is one of the largest alder species in Asia and is identified by its large, broadly elliptical leaves with entire or only finely toothed margins — a trait that sets it apart from the more deeply toothed leaves of most other alders. Its bark is pale gray and relatively smooth on younger trees, becoming more furrowed with age.
It produces notably long, pendulous male catkins and is one of few alders with leaves that are more or less smooth and untoothed. Native to the Himalayan region — including Nepal, Bhutan, northern India, and southwestern China — it grows along river valleys and forested hillsides up to about 3,000 meters elevation.
Japanese Alder (Alnus japonica)
The Japanese Alder is identified by its narrowly elliptical to lanceolate leaves, which are sharply toothed, glossy dark green above, and lighter beneath — noticeably more elongated and narrow than those of most other alder species. Its bark is dark gray-brown and develops vertical fissures with maturity.
It produces slender, cylindrical male catkins that appear in early spring before the leaves. Native to Japan, Korea, northeastern China, and the Russian Far East, it grows in low-lying, waterlogged habitats such as swamps, the edges of ponds, floodplains, and along slow-moving rivers and streams in cool-temperate climates.
Chinese Alder (Alnus cremastogyne)
The Chinese Alder is distinguished by its large, broadly ovate leaves with irregularly double-toothed margins, a glossy dark green surface, and a paler, slightly hairy underside. One of its most notable identification features is its unusually long, pendulous fruiting catkins — the longest of any alder species — which hang in striking, drooping clusters and give it a particularly elegant appearance.
Its bark is gray-brown and becomes moderately furrowed with age. Native to central and western China, particularly Sichuan Province, it grows along streamsides and in moist valley forests, and has been widely planted for timber production and soil improvement.
Manchurian Alder (Alnus hirsuta)
The Manchurian Alder is most readily identified by the conspicuous hairiness of its leaves, shoots, and catkin stalks — a trait perfectly captured in its species name hirsuta, the Latin word for “hairy” or “shaggy.” Its leaves are broadly ovate, sharply double-toothed, dark green above, and densely covered with soft hairs on the underside, particularly along the veins.
The young twigs are also notably hairy. The bark is grayish-brown and furrowed on mature trees. Native to northeastern Asia — including Manchuria, Korea, Japan, and the Russian Far East — it grows in moist temperate forests and along river banks and streams in cold-climate regions.
Seaside Alder (Alnus maritima)
The Seaside Alder stands out from most other alders in a critically important way: it blooms in late summer to early autumn rather than in late winter or spring, making its flowering period an unmistakable identification feature. Its leaves are shiny, dark green, oval to obovate, and finely toothed with a glossy upper surface that is noticeably more lustrous than most alder relatives.
The bark is gray-brown and smooth to lightly fissured. It is a rare species with a highly fragmented native range, found in just three isolated populations — on the Delmarva Peninsula on the U.S. East Coast, along the Ouachita River in Oklahoma, and in a small area of Georgia — making it a species of significant conservation concern.
Thinleaf Alder (Alnus incana subsp. tenuifolia)
Also called the Mountain Alder, the Thinleaf Alder is identified by its thin, papery, ovate to elliptical leaves that feel noticeably less substantial than those of related species — hence the name tenuifolia, meaning “thin-leaved.” The leaves are doubly toothed, dull green above, and paler with soft hairs beneath, especially along the veins.
Its bark is smooth and grayish to reddish-brown. It typically grows as a large shrub or small tree. Native to western North America, it ranges from Alaska and the Yukon south through the Rocky Mountains into New Mexico, growing along mountain streams, in moist valley bottoms, and on the edges of subalpine wetlands.
Smooth Alder (Alnus serrulata)
The Smooth Alder, also known as the Hazel Alder, is identified by its smooth, grayish-brown bark studded with pale, horizontal lenticels — similar to the Speckled Alder but generally smoother. Its leaves are obovate to broadly elliptical, finely and singly toothed (the species name serrulata refers to the fine, saw-like teeth), dark green above, and slightly hairy beneath particularly along the veins.
It typically grows as a multi-stemmed shrub or small tree. Native to the eastern United States, it is found from Maine and southern Ontario south to Florida and Texas, growing in wet riparian habitats including stream margins, swamp edges, and moist wooded floodplains.
Caucasian Alder (Alnus subcordata)
The Caucasian Alder is identified by its large, broadly ovate, almost heart-shaped (subcordate) leaves — among the largest leaves in the genus — which are finely toothed, deep green and somewhat glossy above, and paler with tufts of hair in the vein axils beneath. Its bark is grayish-brown and becomes moderately furrowed on mature specimens.
It is a tall, handsome tree with a notably upright, vigorous growth form. Native to the Caucasus region — including Georgia, Azerbaijan, Armenia, and northern Iran — it grows in moist mountain forests and alongside rivers and streams. It has been introduced in parts of western Europe as both an ornamental and a forestry species.
Oregon Alder (Alnus oregona)
Widely considered synonymous with the Red Alder (Alnus rubra) by most modern botanists, the Oregon Alder is identified by the same field marks: thin, pale bark revealing reddish inner wood when cut, oval leaves with rolled-under margins and coarse teeth, and persistent woody fruiting catkins.
Younger trees have notably smooth, pale gray to whitish bark that can resemble birch at a distance, while older trees develop more textured surfaces. Specifically associated with the river corridors, floodplains, and temperate rainforests of Oregon and Washington State, it is one of the most ecologically important trees of the Pacific Northwest, supporting aquatic ecosystems and salmon habitat.
European Green Alder (Alnus viridis subsp. viridis)
This European subspecies of Green Alder is identified by its bright, glossy green, ovate leaves with sharply double-toothed margins and a relatively smooth surface on both sides — lacking the hairiness found in many other alder species. Its male catkins emerge in spring simultaneously with the leaves, rather than in late winter before leafing out, which is a useful distinguishing trait.
It grows as a dense, sprawling shrub rather than an upright tree. Native to the mountain ranges of central and southern Europe — including the Alps, Carpathians, and Apennines — it colonizes steep alpine and subalpine slopes, rocky stream edges, and recently disturbed terrain including avalanche tracks and glacial moraines.
Formosan Alder (Alnus formosana)
The Formosan Alder is identified by its ovate to elliptical leaves that are sharply double-toothed, bright green above, and paler beneath with soft hairs along the midrib and veins. Its bark is grayish-brown and relatively smooth on young trees, becoming finely cracked and furrowed in older specimens.
It produces slender, erect to slightly pendulous fruiting catkins typical of the genus. Endemic to Taiwan — the island formerly known as Formosa, from which it takes its name — it grows in mountainous forest habitats at elevations between 500 and 2,500 meters, typically along streams and in moist valley forests, and is an important species for soil conservation and reforestation on the island’s steep hillsides.
Andean Alder (Alnus acuminata)
The Andean Alder, also called the Mexican Alder or Aliso, is identified by its long, narrowly ovate to lanceolate leaves with a distinctly acuminate (long-pointed) tip — the feature reflected in its species name — and finely double-toothed margins. The leaves are dark green and glossy above, lighter and slightly hairy beneath.
Its bark is grayish-brown and becomes furrowed and somewhat scaly with age. Native to the mountainous regions of Central and South America — from Mexico south through Guatemala, Colombia, Ecuador, Peru, Bolivia, and into northwestern Argentina — it thrives in cool, moist cloud forests and Andean valleys at elevations from 1,500 to over 3,500 meters, where it is widely used in reforestation and agroforestry.
Spaeth Alder (Alnus × spaethii)
The Spaeth Alder is a hybrid between the Japanese Alder (Alnus japonica) and the Caucasian Alder (Alnus subcordata), and is identified by its strikingly large, broadly ovate to almost heart-shaped leaves that are dark, glossy green above and conspicuously purple-tinted when young — a feature that makes it one of the most visually distinctive alders.
The bark is smooth and gray-brown. It is a vigorous, fast-growing tree with an upright, columnar habit. It does not occur naturally in the wild but is a cultivated hybrid widely planted as an ornamental and street tree across Europe and temperate parts of North America, valued for its striking foliage and adaptability to urban conditions.
Black Alder (Alnus glutinosa ‘Imperialis’)
This is a cultivated ornamental form of the Common Alder, distinguished from the species by its deeply and elegantly dissected, feathery leaves that are cut nearly to the midrib into narrow, finger-like lobes, giving the tree a lacy, fern-like appearance quite unlike any other alder.
The bark and overall form are similar to the parent species — dark gray-brown and furrowed — and it retains the characteristic woody, cone-like catkins. While not a naturally occurring wild tree, it is widely planted in parks and gardens across Europe and temperate North America near ponds, streams, and water features, where the delicate foliage reflects beautifully on the water’s surface.
Seaside Alder (Alnus maritima)
A rare and geographically unusual species, the Seaside Alder has a highly disjunct native range, found in three isolated populations: the Delmarva Peninsula on the eastern coast of the United States, along the Oachita River in Oklahoma, and in Georgia. Unusually for an alder, it flowers in late summer to early autumn rather than spring. It is listed as a species of conservation concern in several states due to its limited distribution.
The Oklahoma population of the Seaside Alder is sometimes treated as its own subspecies (Alnus maritima subsp. oklahomensis) and can be distinguished from the eastern coastal populations by subtle differences in leaf shape and texture. The leaves of the Oklahoma form are slightly broader and the tree tends to have a more shrubby growth form.
Like all Seaside Alders, it flowers in late summer, which remains the most reliable identification trait. Found only along the Ouachita River drainage in Oklahoma, this highly restricted population is considered one of the most geographically isolated and botanically unusual alder populations in the world.
Italian Alder ‘Laciniata’ (Alnus cordata ‘Laciniata’)
This ornamental cultivar of the Italian Alder is identified by its deeply cut, lobed leaves that differ strikingly from the parent species’ smooth, heart-shaped foliage, lending the tree a more textured and architectural appearance. It retains the large, distinctive cone-like fruiting catkins of the Italian Alder, which are among the largest of the genus and persist on the branches well into winter, providing year-round interest.
Like its parent, it has smooth, grayish bark and an upright growth habit. Derived from the species native to southern Italy and Corsica, this cultivar is grown as an ornamental across Europe and temperate regions worldwide, and performs well in a variety of soils including dry and alkaline conditions.