Trees with serrated edge leaves

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What Is An Alder Tree: Information About Alder Trees

Alder trees (Alnus spp.) are often used in reforestation projects and to stabilize soil in wet areas, but you seldom see them in residential landscapes. Nurseries that cater to home gardeners rarely offer them for sale, but when you can find them, these handsome plants make excellent shade trees and screening shrubs. Alders have several distinctive features that keep them interesting throughout the year.

Alder Tree Identification

The easiest way of recognizing an alder tree is by its distinctive little fruiting body, called a strobile. They appear in fall and look like 1-inch long cones. Strobiles remain on the tree until the following spring, and the small, nutlike seeds they contain supply winter food for birds and small mammals.

The female flowers on an alder tree stand upright at the ends of the twigs, while the male catkins are longer and hang down. The catkins persist into winter. Once the leaves are gone, they add subtle grace and beauty to the tree, softening the appearance of the bare branches.

Leaves provide another method of alder tree identification. The egg-shaped leaves have serrated edges and distinct veins. A central vein runs down the center of the leaf and a series of side veins run from the central vein to the outer edge, angled toward the leaf tip. The foliage remains green until it drops from the tree in fall.

Additional Information About Alder Trees

The different types of alder trees include tall trees with single trunks and much shorter, multi-stemmed specimens that can be grown as shrubs. Tree types grow 40 to 80 feet tall and include the red and white alders. You can distinguish these two trees by their leaves. The leaves on a red alder are tightly rolled under along the edges, while those on a white alder are more flat.

Sitka and thinleaf alders reach heights of no more than 25 feet. They can be grown as large shrubs or small trees. Both have multiple stems arising from the roots and you can tell them apart by their leaves. Sitkas have very fine serations along the edges of the leaves, while thinleaf alders have coarse teeth.

Alder trees can extract and use nitrogen from the air in the same way that legumes, such as beans and peas, do. Since they don’t need nitrogen fertilizer, they are ideal for areas that aren’t regularly maintained. Alders are well-suited to wet sites, but abundant moisture isn’t necessary for their survival, and they can also thrive in areas that experience occasional mild to moderate drought.

Alder (Alnus)

  • Alternate, egg-shaped leaves with serrated or doubly serrated margins
  • Small woody cones about 1″ long
  • Commonly found in moist areas next to water

Alders like moist surroundings and there are few creeks in western Oregon not overhung by them. Their peculiar woody cones (called strobiles) identify alders as surely as a flat tail identifies a beaver. They hang from the tree throughout winter like miniature lanterns. Alder leaves are shed while still green. Alders add nitrogen to the soil in the manner of legumes, and decomposing alder leaves improve soil structure.

Eight species of alder are native to North America; Oregon has four: red, white, Sitka, and thinleaf, but only two commonly reach tree size – and only red alder is abundant. Knowing their ranges and leaf traits will help in separating one species from another.

Large tree:(40′-80′ tall; single trunk)

red alder: look for leaf margins that are tightly rolled under.

white alder: leaf margins are not rolled under.

Shrub or small tree: (under 25′ tall; multiple trunks)

Sitka alder: leaf margins have very fine serrations; margins not rolled under.
This species will not be described further.
thinleaf alder: leaf margins have a double set of coarse teeth; margins not rolled under. This species will not be described further.

For more information on the alders native to the Pacific Northwest, go to the species page or see “Trees to Know in Oregon”.

Time once again for another in my British trees series, and I’m going to take a look at the alder…

“Its very existence seems to hang on the proximity of water.”

Gertrude Clarke Nuttall, ‘Trees and How They Grow’

If you’re walking along a river bank or by the side of a loch, it’s most likely that you will come across a grove of alder trees. Alders aren’t spectacular in the way that oak or beech trees can be: they don’t grow to a massive size, nor do they display brilliant colours in autumn. What they have is a strong affinity for water, and this element is woven into their life cycle as well as their properties.

Alnus glutinosa, the common or black alder, is the only native alder in Britain. It is widespread across most of Europe, and its range extends eastwards across Russia to Siberia, and south to Turkey and Iran. It was introduced to North America, probably in the 1600s, and has become naturalised in eastern Canada.

Alders by Loch Caolisport, Kintyre

Alders by Loch Etive

To ecologists the alder is a pioneer species, being one of the first trees to colonise clearings in a forest. Rarely does it grow to more than 70 feet or live longer than 150 years. This is a true water-lover, hugging the banks of rivers and lochs, and flourishing in damp meadows and boggy areas: if its roots are in water, the alder is happy.

Alder is monoecious, producing male and female flowers on the same tree. “Clusters of new and pointed female catkins typically develop over winter. These expand into green, cone-like structures during summer, blackening over winter. They release their tiny seeds the following year.” (Gabriel Hemery, ‘The New Sylva‘) More showy are the dangling male catkins, golden lambs’ tails that look like hazel at first glance – but on closer inspection you’ll see they are slightly shorter than hazel catkins, and more compact.

Old female cones (brown); new female catkins (small and upright, greenish) and male catkins (long, greenish yellow)

Female catkins ripening into cones. The twigs are sometimes sticky to the touch, hence the name ‘glutinosa’.

Female cones in winter

“When the seeds fall ripe from the parent tree and are seeking a lodgment, they are not furnished with wings or parachutes for flight, as are those of the sycamore or the poplar; but they are provided with airtight cavities inside their walls, so that they will float unharmed along the surface of the stream or lake… Sometimes they may be in the water all the winter; sometimes they do not fall till the spring, and their voyage is short; but one day it ends – perhaps the stream subsides a little – and they drift to the shore, and there in the soft mud they may germinate.”

‘Trees and How They Grow’ by G Clarke Nuttall (1913)

The oval – almost pear-shaped – leaves of alder are quite distinctive, being indented rather than pointed at the tip, which makes them easy to distinguish from hazel. They are bright green and deeply veined, often with a serrated edge.

While the mature bark can be brown or dark grey, young alder branches are smooth and often greenish in colour. New shoots may sprout naturally from the base of the trunk. Alder trees are often found in the company of birch and willow.

Lichen on alder trunk

Alder is a food plant for several moths including the delightfully named alder kitten (its head, body and legs are just as furry as you’d imagine); alder catkins are an early source of nectar and pollen for bees, and the seeds are eaten by birds such as siskins and redpolls.

Alder with catkins near Keills Chapel in Knapdale

The alder has an important symbiotic relationship with a bacterium, Frankia alni, which forms nodules on its roots. These absorb nitrogen from the air and make it available to the tree; in return, the alder provides the bacteria with carbon. In this way, alder improves the fertility of the soil where it grows, creating nutrients for species that follow it onto new ground: “The nitrogen-fixing nodules on the alder’s roots improve soil fertility and so make this tree ideal for reclaiming degraded soils and industrial wastelands…” (Trees for Life)

“There are a sort of husbands who take excessive pains in stubbing up their alders, where-ever they meet them in the boggie places of their grounds, with the same indignation as one would extirpate the most pernicious of weeds; and when they have finished, know not how to convert their best lands to more profit than this (seeming despicable) plant might lead them to, were it rightly understood.”

John Evelyn, ‘Sylva’, 1664

The Crannog Centre, Loch Tay

As a wood, the great strength of alder is its resistance to decay, even under water – in fact, once it has been submerged, it gradually becomes as hard as stone. For this reason, ancient people chose it for building tracks and bridges over marshy ground, and crannogs stood on beds made of alder trunks. But once it is taken out of the water and exposed to the air, alder quickly begins to decompose.

“The cities of Venice and Amsterdam were built mostly upon alder timber piles.”

Gabriel Hemery, ‘The New Sylva’

Woods and shoreline south of Ballachulish

The Ballachulish ‘goddess’

In 1880 a small but enigmatic female figure, carved from a single piece of alder with pebbles for eyes, was discovered in a peat bog known as Ballachulish Moss on the shore of Loch Leven. It is thought to date from somewhere between 728 and 524 BC, and is currently on display in the National Museum of Scotland.

Alder trees in place names

In England, names such as Allerton, Allerbeck and Ellerslie recall the existence of an alder wood. The old Gaelic word for alder is ‘feàrn’, and there are plenty of occurrences of this throughout Scotland and Ireland. The author Gavin Maxwell’s house was called Camusfeàrna’, the ‘Bay of Alders’. The Welsh form is ‘gwern‘, sometimes mutated to ‘wern’, and these crop up so often in the east of Wales that historians have wondered whether alder trees were grown there commercially in medieval times, so that their timber could be sold to rich Norman estates in Herefordshire and Shropshire. The theory is that the wood may have been made into clogs for farm workers.

Waterlogged alder woods are called carrs, and this has also been preserved in some English place names.

THE ALDER IN FOLKLORE

‘Sure-hoofed is my steed impelled by the spur;
The high springs of alder on thy shield;
Bran thou art called, of the glittering branches.

Sure-hoofed is my steed in the day of battle:
The high sprigs of alder are in thy hand:
Bran thou art, by the branch thou bearest
Has Amaethon the Good prevailed!”

Traditional Welsh englyn associated with the Cad Goddeu (‘The Battle of the Trees’) in the Book of Taliesin

In the Welsh Mabinogion, the alder tree is the emblem of the Celtic giant-god, Bran. One story tells how Bran’s sister, Branwen, was being mistreated by her husband, Matholwch, the King of Ireland. Bran calls his men together and sets off to rescue her; when they come to the River Llinon, they find that the only bridge has been dismantled on the orders of the Irish king, so Bran lies down across the river to allow the men to pass over his body. This may be a reference to the alder’s natural empathy with water.

Alder was the tree of prophecy and sacrifice, and a shield made from its wood was believed to imbue the carrier with ferocity and protection in combat. Once it has been cut down, the pale wood of alder turns deep orange and releases an orange-red sap, and it may have been this phenomenon that convinced early warriors of its power: to them, it appeared that the alder’s spirit was bleeding and would thus prevent them from being wounded themselves. Warriors became deeply attached to their shields; in Irish mythology they were given individual names and believed to have magical powers in their own right.

However much they loved the qualities of its wood, the Irish considered it unlucky to pass an alder tree on a journey. This may derive from the fact that alder groves were usually dark, boggy places where evil spirits were thought to dwell. Given the widespread distribution of alder, I’m guessing that this must have led to some pretty roundabout routes! And just to compound the problem, it was also believed that putting some alder leaves in your shoes at the start of a long walk would cool the feet and prevent soreness. Plenty of careful planning must have been the secret here!

Deirdre of the Sorrows…

According to an Irish legend, the royal storyteller at the court of King Conchobar mac Nessa had a beautiful daughter named Deirdre. She was destined to marry the King, but she fell in love with Naoise, a handsome warrior. To escape the King’s wrath, Deirdre and Naoise fled across the sea to Scotland where they hid in the alder woods of Glen Etive.

But there was no happy ending: they were tracked down by Conchobar’s men who murdered Naoise and brought Deirdre back to Ulster where she was forced into marriage. One version of the story says that she took her own life by throwing herself from a chariot. Is there any more romantic name than Deirdre of the Sorrows?

Dyes made from alder flowers were once used to colour fabric for garments, and folklore says that fairies’ clothes were dyed with alder pigment to conceal them from human eyes. Three colours could be obtained: brown from the twigs, red from the bark and green from the flowers. Both the bark and the wood contain tannin, used for tanning leather.

Alder burns with an intense heat, making it an ideal fire for forging weapons, and some Bronze Age archaeological finds have revealed the use of alder to make charcoal. Smoke from alder fires was used for divination, as was the movement of the flames. On the living tree, omens were seen in the way the branches moved in the wind, and heard in the rustle of its leaves. Whistles made from alder wood are said to summon the wind and enlist the help of benevolent water spirits.

Since 1956, the guitar manufacturer Fender has been using alder to build the bodies of its electric guitars, including the legendary Stratocaster. (To be precise, the species used is the red alder, Alnus rubra, native to the west coast of America.) But who knew that the unmistakeable notes of Mark Knopfler and Eric Clapton owed their tone to alder wood? Fender’s website explains: “It has a resonant, balanced tone brighter than other hardwoods… It imparts excellent sustain and sharp attack.”

Fresh alder leaves are said to make a good insect repellent, although I haven’t tried it myself. As a treatment for rheumatism, dried alder leaves may be placed in a bed or sewn into a cushion. It has antibacterial properties, and herbalists have prescribed it as a gargle for a sore throat. A decoction of alder bark was traditionally used to treat burns, wounds and inflammations, and alder tree essence is said to relieve anxiety and nervous tension.

“The alder is of all other the most faithful lover of watery and boggie places, and those most despised weeping parts, or water-galls of forests…”

John Evelyn, ‘Sylva’

Sources:

  • Woodlands.co.uk
  • Trees for Life
  • The Woodland Trust
  • The Goddess Tree
  • National Museum of Scotland
  • BBC News
  • UK Moths
  • RCAHMS Canmore
  • Fender Guitars
  • ‘The New Sylva’ by Gabriel Hemery & Sarah Simblet (Bloomsbury, 2014)
  • ‘Trees and How They Grow’ by Gertrude Clarke Nuttall (1913)
  • ‘Celtic Tree Magic: Ogham Lore and Druid Mysteries’ by Danu Forest

Photos copyright © Colin & Jo Woolf

More in my British trees series…

  • The darkness of the yew
  • The wisdom of the oak
  • The Scots pine: keeper of the forest
  • Hawthorn: bride of the hedgerow
  • The enchantment of the rowan

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Deciduous Trees

The restored woodland areas are mostly planted with native hardwoods to re-create the Big Woods habitat that existed in the area originally. This “Big Woods” region has been diminished to only small remnants of what it once was. Twenty species of native hardwoods have been planted, including oaks, maples, ash, walnut, etc.

Ashes

Green Ash (Fraxinus pennsylvanica)

Leaf Description: Opposite compound on stem, length 8” to 12”. Contains five to nine sharp-pointed leaflets; dark green and smooth above, pale green or whitish beneath.

Distinguishable Traits: Long, winded seeds (samara) that resemble canoe paddles growing in a clump. Bark is greenish-brown on older trees with narrow ridges separated by deep diamond-shaped fissures.

White Ash (Fraxinus americana)

Leaf description: Very similar to green ash with longer leaflets. Leaves often turn red in autumn.

Distinguishable Traits: Among the last trees to leaf out in the spring.

Basswoods

American Basswood – Tilia americana

Leaf Description: Simple, alternate on stem, length 3” to 6”. Heart shaped, saw toothed with sharp point at top. Turns yellow or orange in autumn.

Distinguishable Traits: Thick crowns cast a deep shade on the ground underneath. Basswood produce small rounded fruits attached in clusters, often have multiple trunks with light gray and smooth bark.

Cherries

Black Cherry – Prunus serotina

Leaf Description: Simple, alternate on stem, length 2” to 6”. Oval or lance shaped with finely toothed margins. Shiny above, paler below.

Distinguishable Traits: Smaller tree with an irregular crown. Notable drooping clusters of pea-sized cherries.

Choke-cherry – Prunus virginiana

Leaf Description: Simple, alternate leaves that are egg shaped with.

Distinguishable Traits: Grows in multiple stems that are normally 7-16 ft. tall.

Elms

American elm – Ulmus americana

Leaf Description: Simple, alternate on stem, length 4” to 6”. Asymmetrical shape, dark green, generally rough above, smooth below. Veins are very pronounced, running in parallel lines from mid rib to edge of leaf.

Distinguishable Traits: Wide, spreading branches that droop at the ends; crown is vase shaped. Dark, ashy gray bark that comes off in flakes. Bark has varying colors in cross section if broken in half.

Slippery Elm – Ulmus rubra

Leaf Description: Simple, alternate on stem, asymmetrical shape. Prominent veins on leaf, sandpapery texture both above and below the leaf.

Distinguishable Traits: Leaves are usually larger and wider than those found on American Elm. Twigs and buds are known for their hairiness, as opposed to the smooth American Elms.

Hackberries

Hackberry – Celtis occidentalis

Leaf Description: Simple, alternate on stem, length 2” to 4”. Has long, narrow, tapering points. Uneven at base with prominent veins and hairy on the upper side.

Distinguishable Traits: Limbs are often crooked and angular, with short, bristly stubby twigs. Bark is grayish brown with prominent, short, corky ridges. Holds thin, purplish berries.

Hickories

Bitternut Hickory – Carya cordiformis

Leaf Description: Alternate compound on stem, length 6” to 10”. Contains 7-11 leaflets that are bright green with finely toothed edges.

Distinguishable Traits: Notable bright yellow winter buds. Leaves are the smallest among the hickory species. Bark is granite-gray, faintly tinged with yellow and broken into thin, plate-like scales.

Ironwoods

Ironwood – Ostrya virginiana

Leaf Description: Simple, alternate on stem, length 2” to 4”. Oblong with narrow tip; sharp doubly toothed margins. Dark, dull, yellow-green above and light yellow green below.

Distinguishable Traits: Shorter tree, branches are long and slender, drooping at the ends. Fruit occurs in culsters (catkins) resembling those of the common hop vine.

Maples

Boxelder – Acer negundo

Leaf Description: Opposite compound on stem with three leaflets, length 5” to 8”. Smooth with irregularly toothed margins.

Distinguishable Traits: The trunk is rarely strait for any length, often having a leaning and twisted appearance and quickly branching into several major limbs. The fruit (paired samaras) spin like propellers when they fall in autumn.

Red Maple – Acer rubrum

Leaf Description: Simple, opposite on stem, length 2” to 4”. Either three or five pointed saw toothed lobes. Upper surface is light green, lower surface is whitish. The first maples to turn brilliant shades or red, orange and yellow in autumn.

Distinguishable Traits: The shortest of the common maple trees. Seeds consist of two connected red winglets (samaras). Leaves either appear as the classic Canadian flag shape or as a distinct thee lobed leaf.

Silver Maple – Acer saccharinum

Leaf Description: Simple, opposite on stem, length 4” to 6”; three to five points ending in long points with deep angular openings. Pale green on upper surface and silvery underneath. Pale yellow or orange in autumn.

Distinguishable Traits: Long, thin lobed, slivery leaves. Gray bark that peels off in long scales.

Sugar Maple – Acer saccharum

Leaf Description: Simple, opposite on stem, length 3” to 5”; three to five pointed. Dark green on upper surface, lighter green underneath. Turns dark red, scarlet, orange or yellow in autumn.

Distinguishable Traits: Similar to the Red maple’s classic Canadian flag style leaf. Distinct connected green winglets (samaras) containing 2 seeds, easily carried by the wind.

Oaks

Bur Oak – Quercus macrocarpa

Leaf Description: Simple, alternate on stem, length 6” to 12”. Crowned at end of twigs with deep indentations near base.

Distinguishable Traits: Noticeable crown on end of leaves, gnarled branches covered with corky tissues.

Red Oak – Quercus rubra

Leaf Description: Simple, alternate on stem, length 5” to 9”, divided into seven to nine lobes. Each lobe is coarsely toothed with bristle tips.

Distinguishable Traits: Tall trees with distinguishable oak leaves that have “pointy” lobes. Acorns are abundant on the ground around the tree. Trees contain light gray, shallow fissures in the bark.

White Oak – Quercus alba

Leaf Description: Simple, alternate on stem, length 5” to 9”. Leaves are crowded towards ends of twigs, deeply divided into fingerlike lobes with rounded tips. Leaves often remain on tree most of the winter.

Distinguishable Traits: Rounded leaf lobes, grows short in the open or tall and narrow in the forest.

Poplars, Aspens, and Cottonwoods

Cottonwood – Populus deltoids

Leaf Description: Simple, alternate on stem, 3” to 5” long. Broadly triangular, finely toothed or wavy edges. Covered with soft white hairs on underside.

Distinguishable Traits: Notable seeds cotain thin capsules “catskins”, that are set free in late May or June. Enclosed within is a cluster of white cottony hairs that carry the sees long distances.

Quaking Aspen – Populus tremuloides

Leaf Description: Simple, alternate on stem. Small, broadly oval with short point at end and finely toothed along edge. Leaves turn brilliant yellow in autumn.

Distinguishable Traits: Thin, white to gray green bark. Bark can become grayish and warty. Leaves appear to quake or “wave” at you in a very slight breeze.

Walnuts

Black Walnut – Juglans nigra

Leaf Description: Alternate compound on stem, length 12” to 14”. Contains 14-22 yellow green, sharply pointed leaflets, tapered at the ends, smooth above, pale and hairy underneath.

Distinguishable Traits: Large distinct leaves with large rounds nuts in a solid green husk. Bark is thick and very dark brown with deep fissures into rounded ridges.

Alder Tree Stock Photos and Images

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  • Big Sur California USA Alder tree impression Big Sur California
  • Single alder tree in a field on the South Downs with large cumulus clouds and blue sky in late summer in West Sussex England UK
  • Black Alder, European Alder or Common Alder Tree, Alnus glutinosa, Betulaceae
  • Common Alder tree by stream, Elterwater, the Lake District, Cumbria, England.
  • Blossom of the alder tree isolated on white
  • Black alder tree, Hokkaido
  • Grey alder tree – view from below
  • Close up of Moss and Lichen growing on an Alder tree.
  • Alder tree in winter, UK
  • Fresh deciduous stand with old alder tree in foreground and broken one in background,Bialowieza Forest,Poland,Europe
  • Mount Baker-Snoqualmie National Forest, WA; Red alder (Alnus rubra) trunks with fall colors of vine maples (acer circinatum)
  • Common Alder on the edge of Scar House Reservoir, Nidderdale, North Yorkshire.
  • Lone alder tree at coast in early springtime with ice still left on the lake
  • grey alder tree isolated on white background
  • Grey Alder, Gray Alder (Alnus incana), twig with leaves and fruit, studio picture.
  • The Hare and Billet pond, Blackheath
  • Red Alder Alnus rubra Quinault Olympic National Park Washington United States
  • Trunk of birch tree in front of alder trunks.
  • USA, Oregon, Siuslaw National Forest. Cape Perpetua Scenic Area, Grove of red alder (Alnus rubra) trees in fog.
  • Red alder tree washed up on Rialto Beach. Yes that is the real color 🙂 I always find it stunning.
  • Single alder tree in a field on the South Downs with large cumulus clouds and blue sky in late summer in West Sussex England UK
  • Caucasian Alder and Catkins, Alnus subcordata, Betulaceae, Caucasus, Iran
  • Alder tree trunk. Oregon
  • Alder tree, springtime
  • alder trunks, alnus
  • Tree planting volunteers and woodland winter activities wild adventures
  • Alder (Alnus sp.), Alder swamp with sedges (Carex acutiformis) Darßer Forest, Western Pomerania Lagoon Area National Park
  • Alder trees
  • Alder Tree Catkins Alnus Glutinosa
  • Reeds and alder tree grow in drainage ditch in wet marshy land
  • Male pollen bearing catkins and last year’s female cones on a alder tree Alnus glutinosa in early spring Somerset UK
  • Alder tree branches after blizzard covered by fresh snow
  • Black alder
  • Forest of Red Alder, Alnus rubra in winter at Old Sitka State Historical Park near Sitka, Alaska, USA. Photography by Jeffrey Wickett.
  • Old common black alder tree bark Alnus glutinosa
  • Dusting of snow on male catkins and immature female flowers of an alder, Alnus glutinosa, tree in late winter, March
  • River Tarvasjõgi
  • alder tree in winter at dawn
  • White Alder Tree Forest at Big Santa Anita Canyon, Angeles National Forest, California
  • Freshly cut alder tree, Finland
  • Alder tree reflected in the River Cree
  • Alder tree trunk. Oregon
  • Alder tree, springtime
  • Old hollowed Alder tree, with Kingcups and deposits from iron reducing bacteria, Wales, UK
  • Conifer Cones Of Alder Tree
  • High angle view of alder tree fallen on lake
  • Alder tree twig with catkins at a blurred background
  • Alder Tree on Lakeside, Schweriner Aussensee, Schwerin, Western Pomerania, Germany
  • Alder tree catkins alnus glutinosa
  • Korean history Royal Tombs of the Joseon Dynasty King Sunjo the alder tree forest
  • Primeval deciduous stand of Bialowieza Forest in summer with old alder tree in foreground
  • Silhouetted Alder Tree Skeleton (Alnus glutinosa), on a Misty Winters Day. Exeter, Devon, UK.
  • Male and female catkins of the alder tree, Alnus glutinosa, developing towards the end of January. The long, male catkins can be seen in the left of t
  • Old common black alder tree bark Alnus glutinosa
  • Dusting of snow on male catkins and immature female flowers of an alder, Alnus glutinosa, tree in late winter, March
  • Alder tree (Alnus glutinosa) felled by Eurasian beaver (Castor fiber) within a large wet woodland stream enclosure, Devon, UK, March.
  • Alder tree against misty sky
  • Alder tree growing on the bank of the Bride River, a tributary of the Blackwater River, County Waterford, Ireland
  • Tree fungus on alder tree
  • Grey alder tree – view from below
  • male flowers (catkins) of an Alder tree (Alnus glutinosa)
  • Alder tree, springtime
  • common alder tree during spring
  • Alder (Alnus spec.) buds and leaves emerging in spring, Belgium
  • Alder tree fallen on lake by mountain against cloudy sky
  • Alder tree buds on a twig at natural green background
  • Growing alder trees
  • Yellow flowering earrings of an alder tree Alnus in early spring
  • Alder tree, wetland reed-bed and distant hill near Killin, Perthshire, Scotland, UK
  • Misty morning in alder-carr stand of Bialowieza Forest with alder tree in foreground
  • Silhouetted Alder Tree Branch (Alnus glutinosa) on a Winters Day against a Blue Sky. Exeter, Devon, UK.
  • An example of the Alder sawfly larva, Eriocampa ovata, on an alder tree leaf. North Dorset England UK GB
  • Male greenfinch (Carduelis chloris) perching in an alder tree (Alnus) in Springtime. Devon, UK
  • Dusting of snow on male catkins and immature female flowers of an alder, Alnus glutinosa, tree in late winter, March
  • Alder tree (Alnus glutinosa) felled by Eurasian beaver (Castor fiber) within a large wet woodland stream enclosure, Devon, UK, March.
  • An Alder tree in winter, Warwickshire, UK
  • Old alder tree growing on the bank of the Bride River, a tributary of the Blackwater River, County Waterford, Ireland
  • Close up of female catkins of the Alnus maximowiczii, an alder tree native to east asia. (montane alder)
  • mossy grey alder tree trunk
  • Alder Tree Catkins
  • Alder tree, springtime
  • Nymph of Pantilius tunicatus mirid bug crawling on alder tree. Tipperary, Ireland
  • Alder tree in early summer with vibrant green leaves contrasting sharply with blue sky.
  • High angle view of alder tree fallen on calm lake
  • Male inflorescences (catkins) of black alder tree, common alder, European alder (Alnus glutinosa)
  • Black alder tree growing in the Thaya River Valley, Thayatal National park, Austria
  • Yellow flowering earrings of an alder tree Alnus in early spring
  • Black alder, Alnus glutinosa, tree developing leaves.
  • Natural swampy forest at springtime with old alder tree in foreground
  • Female Alder Tree Catkin (Alnus glutinosa). Exeter, Devon, UK.
  • An alder tree that has fallen in the River Lune and become lodged on a weir near the Crook O’Lune near Caton Lancashire England Uk GB
  • Scenic view of Rime alder tree on peaceful landscape against the sky
  • An alder tree, Alnus glutinosa, tree on the banks of the Kennet and Avon Canal in winter, Hungerford
  • Alder tree (Alnus glutinosa) with trunk heavily gnawed by Eurasian beavers (Castor fiber) with Downy birch trees (Betula pubescens) felled in the background, within a large wet woodland stream enclosure, Devon, UK, March.
  • Alder tree over Gawlik Lake in Masurian Lake District of Warmian-Masurian Voivodeship of Poland
  • Alder Tree Fungus
  • Close up of female catkins of the Alnus maximowiczii, an alder tree native to east asia. (montane alder)
  • Black-capped chickadee perched in a speckled alder tree.
  • Alder Tree Catkins
  • Alder tree, springtime

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Alder Tree Names and Types of Alnus Species

Picture of a Alder Tree


Bark of the Grey Alder Tree (Alnus incana)

The genus Alnus (Alder) belongs to the birch family (Family Betulaceae). This genus is comprised of about 30 species of monoecious Alder trees (of which only a few reach a large size) and shrubs.

All Alder tree species are deciduous. They have flowers that are called catkins with elongated male catkins on the same plant as the shorter wider female catkins. They are often visible before leaves appear, and they are mainly wind pollinated. They differ from birches (Betula, the most similar genus) in that the female catkins are woody and do not disintegrate at maturity, opening to release the seeds in a similar manner to many conifer cones.

The largest Alder species are Red Alder (Alnus rubra) on the west coast of North America and Black Alder (Alnus glutinosa), native to most of Europe and widely introduced elsewhere, both reaching over 30m or 90ft tall. However, the widespread Green Alder (Alnus viridis) is more of a shrub than a tree, rarely reaching 5m or 15ft.

Facts about the Alnus Genus of Trees
  • Genus Latin Scientific Name = Alnus.
  • Genus Latin Name Pronunciation: AL-nus
  • Genus Latin Name Meaning: The ancient Latin name for the Alder tree.
  • Genus Common Names = Alder. List of Alder Vernacular Names
  • Number of Taxa in the Alnus Genus = 31
List of Alder Trees, Alnus Genus – All known species, taxa types, organized by scientific Latin botanical name first and common names second
List of Alder Tree Species Names

Botanical Tree Name Common Tree Name
Alnus acuminata Andean Alder
Alnus cordata Italian Alder
Alnus cremastogyne Long Peduncled Alder
Alnus firma Kyūshū
Alnus formosana Formosan Alder, Formosa Alder
Alnus fruticosa Siberian Alder
Alnus glutinosa Black Alder, European Alder, Common Alder
Alnus incana Grey Alder
Alnus incana ssp. hirsuta Manchurian Alder
Alnus incana ssp. oblongifolia Arizona Alder
Alnus incana ssp. rugosa Speckled Alder
Alnus incana ssp. tenuifolia Thinleaf Alder, Mountain Alder
Alnus japonica Japanese Alder
Alnus jorullensis Mexican Alder
Alnus mandshurica ¡ ?
Alnus maritima Seaside Alder
Alnus matsumurae Honshu (Japan)
Alnus nepalensis Nepalese Alder
Alnus nitida Himalayan Alder
Alnus oblongifolia
(syn. Alnus incana ssp. oblongifolia)
Arizona Alder
Alnus orientalis Oriental Alder, Syrian Alder
Alnus pendula ¡ ?
Alnus rhombifolia White Alder
Alnus rubra Red Alder
Alnus serrulata Hazel Alder, Tag Alder, Smooth Alder
Alnus sieboldiana (オオバヤシャブシ in Japanese)
Alnus subcordata Caucasian Alder
Alnus trabeculosa ¡ ?
Alnus viridis Green Alder
Alnus viridis ssp. crispa Mountain Alder
Alnus viridis ssp. fruticosa Siberian Alder
Alnus viridis ssp. sinuata Sitka Alder, Slide Alder
Alnus viridis ssp. viridis Eurasian Alder


Alder seed catkins (cones) of Alnus incana

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