12 Types of Alder Tree: Identify Leaves, Fruit, Seeds of This “Pioneer” Species

Image of an alder tree (pioneer species) in an oval frame showing its leaves and Alder tree branches up close.

Often referred to as a “pioneer” species, the Alder tree was a crucial asset for Native Americans early on, but it gets that name because of its remarkable properties.

The Alder tree is a pioneer species because as a member of the Birch tree family (closely related to Elms), this tree has the ability to survive in areas that have little or no other vegetation and rapidly help ecosystems develop.

Currently, there are around 35 species of Alder Tree.

Of these, the two most common, the Red Alder and Black Alder have the conservation status of ICUN 3, least concern, same as the Red Oak Tree and other successful species.1

Because this tree has the power to spur plant life and thrive where nothing else can, it’s an important one to cultivate.

This guide explains how to identify various types of Alder trees, as well as the leaves, fruit, and seeds of this species so you can easily spot an Alder tree anywhere.



  • Family: Betulaceae
  • Genus: Alnus
  • Type: Deciduous

IUCN Red List of Threatened Species Ranking

Least Concern


Types of Alder Tree: Alder Tree Identification

Here are some of the different types of Alder Trees, and how you can identify them.


1. Black Alder Tree

The Black Alder Tree, aka the common Alder or European Alder, gets its name from the darkening of its bark that occurs with age. The Black Alder often has sticky leaves.

It is a highly successful pioneer species (occasionally invasive) that thrives in wet environments. It is native across Continental Europe, the UK, Ireland, Northern Africa, and even parts of the middle east.

It can reach heights of 60 feet.


A tall Alder Tree by the road.

(Image: Vilensija21)


A young Alder Tree planted on a grassy field.

(Image: Berserkur20)


2. Red Alder Tree

The Red Alder, aka the Pacific Coast Alder or Alder Tree Oregon, is the most common species in North America. It takes its name from the ruddy color which appears when the bark is lightly damaged.

It can be identified by the margins of its leaves which curl slightly under. It is extremely popular as a hardwood tree, and the bark can be used to derive several color dyes.

It is native to the pacific northwest and can reach heights of 80 feet.


3. Green Alder Tree

The Green Alder is a relatively small species (containing several subspecies) and can even appear as a mere shrub. It has slightly reflective green leaves which can tinge yellow.

This tree is remarkable in that it produces leaves that appear before flowers. Green Alders are native to North America and Europe and can reach heights of 14 feet.

In some environments it has been identified as invasive.10


A photo of an Alder Tree that look like a short shrub.

(Image: Georgi Kunev22)


Photo of the Alder Tree with the sky as its background.

(Image: Mitch Barrie29)


4. White Alder Tree

The White Alder is a fast grower and has been in certain cases seen at over 100 feet, although a standard mature height would be more like 50. Like many other species, the White Alder takes its name from the color of its bark.

It is native to North America.


5. Grey Alder Tree

The Grey Alder, aka the Mountain Alder or Speckled Alder, takes its name from the grayness of its bark and leaf-bottoms. They produce marvelously colored catkins, which can be bright-red or violet, rather than the common yellow.

The Grey Alder is native to North America and thrives especially in the Rocky Mountains. It can reach heights of 35 feet.


Photo of a fully grown Alder Tree on a grassy field.

(Image: AnRo000223)


Photo of an Alder Tree in a well-maintained park.

(Image: Peter O’Connor24)


6. Italian Alder Tree

The Italian Alder is an extremely popular choice for landscaping. It has rounded leaves, which can even look like hearts.

As a landscape Alder, it can grow in poorly draining soil conditions, yet is more drought tolerant than other Alders. As the name suggests, it is native to Corsica and Southern Italy, but can now be found throughout the Southern Mediterranean region.

It can grow to 50 feet, sometimes even 80.


7. Seaside Alder Tree

The Seaside Alder, aka the Beach Alder, is deceptively named because, while it is found in coastal regions of North America, it is not actually found on the coast, but inland. It is also found in central areas of the continent, Oklahoma for example.

This species blooms in the fall, rather than the spring, and has three subspecies. It is native to North America and can reach 30 feet in height.


Close-up photo of the flower of an Alder Tree.

Robert H. Mohlenbrock(Image: Robert H. Mohlenbrock31)


Image of an Alder Tree showing its long trunks and barks.

(Image: Aroche25)


8. Hazel Alder Tree

The Hazel Alder, aka Swamp Alder or Tag Alder, is a small-of-stature species. Its reproductive process is remarkable in that it can clone itself through its suckers.

If left unchecked, it can form a thicket. Hazel Alders are most often found by bodies of water.

They are native to the eastern regions of North America and can reach heights of 20 feet.


9. Mexican Alder Tree

The Mexican Alder is another small variety, it can even stand as a mere shrub. It is usually evergreen or semi-evergreen and is a very popular choice for landscaping.

It stands out with intensely green serrated leaves. This variety is also known to have very aggressive root growth.

Beware if planting that you give it enough space underground. It is native to Central America and can grow above 70 feet tall.


Photo of several Alder Trees at the foot of a mountain.

(Image: Alejandro Bayer Tamayo26)


Photo of the think barks of an Alder Tree by a swamp.

(Image: Michael Kurz30)


10. Oriental Alder Tree

The Oriental Alder, aka the Syrian Alder, is remarkably fast growing. It can grow to a mature height of 30 feet in around ten years.

The leaves are more triangular than other species and dark green and glossy. This tree can closely resemble the Japanese Alder, but it is native to the middle east – Cyprus, Syria, Turkey, Lebanon, Palestine, and Iran.

Here is a short guide from the American University of Beirut.11


11. Himalayan Alder Tree

The Himalayan Alder or Nepalese Alder, has rather soft wood, which can be dried and used for furniture. Like that of other species, its bark can be used to manufacture dyes.

The bark is also favored for herbal remedies by those who tout its anti-inflammatory properties. It is native to Pakistan, Nepal, and the western Himalayan region and can grow up to 60 feet tall.


Photo of a mature Alder Tree showing its bright green leaves.

(Image: Krzysztof Ziarnek, Kenraiz27)


Photo of several Alder Trees in a forest.

(Image: Σ6428)


12. Japanese Alder Tree

The Japanese Alder is a relatively small species which is usually around 25 feet when mature. It has a remarkably dense canopy, and while it is Deciduous, in some climates it lives evergreen.

Like other species, it does well in wet conditions. This one however is uniquely native to Japan, Korea, and China.2


Alder Tree Leaves

Almost all Alders are Deciduous. Young leaves can be sticky and shiny.

Older leaves will usually be of oval shape and have serrated edges, rather than the consistent ones of Dogwood Tree leaves, for example. Red Alder leaves can be from 7 to 15 centimeters long.

Black Alder leaves rarely exceed 10 centimeters in length. They are usually dark green on their upper side, like a Cottonwood Tree leaf, and have a more pale underside.

The Black Alder usually keeps its greenness and leaves late into the autumn. It also does not have shade leaves.

So usually as a Black Alder grows, the lower branches will die off, leaving the tree with an upper canopy and relatively bare trunk.

Alder Tree Blossoms

The Alder produces catkin flowers rather than blossoms. To see an example of a tree with colorful blossoms, check out this article on the pros and cons of Redbud Trees.

Alder Tree Flower

The flowers are catkins – a slim cluster of many flowers with minimal or no petals. One Alder Tree carries both male and female catkins, the males being longer.

They are usually pollinated by wind, but sometimes by bees.

Alder Tree Bark

Alder Trees have scaly bark (like Cottonwood Tree bark). It can range from dark brown in some species to close white in others.

It can be stained, fissured, or covered in lichen. Cracks expand as the tree grows.

Alder Tree Fruit

Once a female catkin is pollinated it gradually hardens and becomes woody, transforming into a small conical fruit. As it matures, the cone opens, releasing the seeds.

Alder Tree Seeds

Alder Tree seeds are usually small, circular, and of dark color. They grow in fertilized Alder cones tree and usually drop at maturity in fall or winter.

Some species will have a membrane margin to facilitate wide dispersal or will have webbing to trap air pockets in order to travel by water.3

Alder Tree Native Habitat

The Red Alder is native to North America. You can find Alder Trees in Washington State, for example, as well as parts of Canada.

The Black Alder is native to most of continental Europe, as well as Great Britain and Ireland. Alders are most usually found in wetlands or by bodies of water.

Alder Tree Height, Canopy and Growing Zones

A Black Alder can grow to up to 60 feet and reds can reach up to 80.

Alder Trees are often pyramidal when young and can have a canopy about 1/3 the width of their height.

Growing zones for Alder Tree (where to grow) vary by species. The Black Alder is hardy in US zones 3-7, and the Red Alder in zones 6-8.

Alder Tree Growth Rate

Growth rate is dependent on species and environment. A Black Alder can grow from around 7.5-16 inches per year until it reaches maturity, and a Red Alder can do similarly.

A 20-year-old Red Alder may be more than 70 feet tall. Saplings can grow up to 10 feet per year.

Alder Tree Facts

Here are some interesting facts about Alder Trees.

Alder Tree Ecology

The Alder Tree is critical to earth’s ecosystem. For example, butterflies and moths feed on their leaves and catkins.

Perhaps its most interesting ecological contribution is ‘nitrogen fixation.’ The Alder has a symbiotic relationship with Frankia alni, an actinomycete, filamentous, nitrogen-fixing bacterium.

Close-up photo of the flowers and seeds of Alder Tree hanging on its branches.

(Image: Annette Meyer16)

This bacterium basically takes nitrogen out of the air and makes it available to the Alder. The tree, in return, provides the bacterium with carbohydrates produced through photosynthesis.

Thus Alders help make large quantities of essential nitrogen available to the local ecosystem.1

Even after Alders die, as snags they provide homes for various birds, or dens for reptiles, amphibians, and fish Because of common proximity to water, the dead tree releases nutrients into the water that can spread to support a vast array of life.

Alder Tree Symbolism

One use of the Alder image is on the coat of arms of the Austrian town Grossarl. The design was adopted in 1965.

It symbolizes both the local ecology and wood industry. The tree has also been said to represent with its roots a cultural rooting, and with its leaves proliferation of the community’s children.

In England green dye from the Alder was used to color the clothing of woodsman. In Irish folklore, passing an Alder Tree during a journey was considered bad luck.4

Pioneer Species

A loose definition of pioneer species is one that is among the first to populate a barren ecosystem. For example, in 1980 after the volcanic eruptions at Mount Saint Helens, much of the local ecosystem was wiped out.

Some animals and root systems survived underground beneath the ash, but pioneer species like the Alder were largely responsible for restoring life to the area. Over time a desolate ground can become a beautiful Alder landscape.

What Does an Alder Tree Look Like?

Alders are most often found in wetlands or by bodies of water. Alder leaves are often sticky and shiny.

Mature ones will be rounder and have serrated edges. In the fall, those of many species turn brown instead of yellow or red.

Photo of a beautiful Alder Tree in the middle of a field.

(Image: AnRo000217)

The flowers are catkins which are often but not always yellow. Individual trees have both male and female catkins, of which the males are usually longer.

In the fall they become seed cones. Alder bark is usually dark and develops cracks as the tree matures.

How To Stop Alder Tree Disease: Alder Tree Disease Prevention

The most concerning disease affecting Alder Trees today is infection by an oomycete called Phytophthora alni.12 It causes conditions that manifest as root or collar rot.

It is believed to have originated recently, perhaps as a crossbreed or hybrid between other species. Today P. alni has spread across Europe and has recently been found in North America.

The first discovery of this pathogen was in Britain. Since then, it has been reported in regions mostly with high moisture and less light.

Think Central Western Europe and Alaska. P. alni has three subspecies, but P. alni is considered the standard.

It appears most commonly and is most virulent.

It has both sexual and asexual methods of reproduction, although it is suspected to spread predominantly with the former.

In the wild, P alni has only been seen to affect Alder Trees – specifically, the Italian Alder Tree, the Black Alder, the Grey Alder, and the Green Alder. But greenhouse trials have shown that other trees like Walnut Trees, American Chestnut Trees, and Wild Cherry Trees, are also vulnerable.

How To Identify

Most of the time, affected trees will have unusually few and small leaves. The leaves may also take on a yellowness and will likely fall early in the season.

After many years, branches on the tree’s crown can begin to die. The most distinctive marks are dark red spots at the base of the trunk.

These are indicative of phloem death. (Phloem is the vascular tissue of the tree.)

The severity of infection varies greatly. In some cases P. alni will cause a quick death, however, in others, the Alder may continue living for years, deteriorating abnormally fast P. alni is considered to be a serious threat to European and North American woodlands which lie adjacent to bodies of water.5


Unfortunately, there is no known method of treatment. Removing dead or dying trees can actually just spread the P alni.

However there is some evidence that, if infection is caught early, coppicing the tree can be of some benefit. This means that in winter you cut the tree down to around just 25 centimeters above the ground.

Then allow it to grow out anew the following spring.6

Geographical risk factors for P. Alni include proximity to large, fairly warm slow-flowing bodies of water, and the presence of clay loam soil or more generally, soil with finer texture.

Common Pests of the Alder Tree

The particular pests that could beset an Alder Tree depend on the species and location. For example, Flat Headed Borer Beetles attack White Alder Trees.

Close-up photo of the pest infesting the bark of an Alder Tree.

(Image: San Bernardino Nat’l Forest18)

The best way to tell if your tree is suffering from pests is simply to type specific symptoms into Google and check against location and tree species. Or if you can see the pest, and are confident it is culpable, you can type its features into google.

Once you have identified the pest, you can consider natural pest control for Alder Tree. This, again, will depend on the specific case.

In the case of the Borer Beetle that besets White Alders, simple pruning is a safe and effective solution. If you are looking for a substance application, check out this list of horticultural oils.13

How Much Carbon Does Alder Tree Sequester?

In many places, Alders account for a lot of forest carbon sequestration.14 It is suggested that typical hardwood trees can sequester up to 48 pounds of carbon per year.

Calculating most carbon values like the carbon footprint of timber or the carbon footprint of wood-burning stoves, the calculation for a single tree can only be a very rough estimate.

To get a better idea of the capacity of a specific tree, consider using a carbon calculator.

What Is Alder Wood?

Alder Trees produce one of the most versatile types of wood in the world. It has multiple applications.

It is favored in the manufacture of guitars, alongside that of the Basswood Tree, and in leather tannins. However, its most popular application is probably as furniture.

Where Does Alder Wood Come From?

In North America, Alder wood is almost always taken from Red Alders. Buyers should always ask suppliers about ethical sustainability practices.

For more information, look at this complete guide on Red Alder wood.15

Knotty Alder Wood

‘Knotty Alder’ is a common label used to describe Alder hardwood that has frequently visible knots. It is a popular choice for home and furniture applications and can be found at most home goods stores.

Alder Wood Cabinets

Alder wood cabinets are an excellent choice for a house, especially for a kitchen. It takes stains exceptionally well, so can be made to respond to a variety of interior design schemes.

It has the highest hardwood lumber grade, a superior grain to cherry wood, and is remarkably light. Its biggest shortcoming is probably that it doesn’t do well with direct exposure to water, though overall it is remarkably sturdy and reliable.

Plus Alder wood products are usually more sustainable than others made with Meranti wood for example.7

Alder Wood for Smoking

Alder wood smoke can be used to prepare foods like coffee and fish.

Also, the tree’s inner bark, as well as Red Osier Dogwood, has been used by some Indigenous peoples of the Americas in smoking mixtures.

Growing an Alder Tree

Growing Alder Tree from a seed is a relatively straightforward process. First, take a mature cone from an Alder Tree at the beginning of winter.

Lightly shake or tap the cone to release the seeds.9 Then distribute them on a seed tray filled with a few inches of half compost and half soil mixture.

Cover the seeds with a slight layer of the soil mixture. Keep them moist and covered in a greenhouse environment through the winter, and by spring you should have a seed-tray full of Alder seedlings!

Close-up photo of a very young Alder Tree sprouting from the ground.

(Image: Krzysztof Ziarnek, Kenraiz19)

Growing an Alder Tree from a seedling stage is also straightforward. Prepare the location for your seedling by clearing any present weeds.

Dig a hole big enough for the entire root group.

Then simply place the seedling into the hole and firm it in the soil. Well, water.

Growing an Alder Tree from a cutting is not typically attempted.

When to plant Alder Tree for the best yield can vary, so another method involves picking green seed cones in the fall and drying them in a metal container somewhere warm, all winter. Then in early spring, soak the seeds in water up to two days, then sow them as normal in April.

How much sunlight does Alder Tree need each day? How long it takes to grow Alder Tree?

The best-growing conditions for Alder Tree, and watering needs for Alder Tree plants all depend on the species and environment.

Because of the Alder’s unique nitrogen-fixing abilities, the best companion plants for growing Alder Tree should include those that love nitrogen, like leafy greens. Plant some varieties a couple of meters away from the base of your maturing Alder Tree and watch them flourish!8

Planting Tips for Alder Tree

How far apart to plant Alder Tree mostly depends on the type of space you want to create. You can plant an extremely dense group and assume a low survival rate.

You can also space them a few feet apart. They commonly grow in groves.

If you are worried about your Alder Tree overshadowing lower plants, three yards spacing is recommended.

Frequently Asked Questions About Alder Tree

How Do Alder Trees Influence Spruce Tree Growth?

The nitrogen-fixing qualities of the Alder Tree help it improve the productivity of plants in its vicinity.


What Is Shadowhunters Alder Tree?

This refers to a character named Alder Tree from a TV show called Shadowhunters.


Can Alder Trees Have Red Berries?

Alder Trees do not produce red berries. To help identify your tree, look at this article on Red Berry identification.


Read More About Alder Tree


1Wikipedia. (2023, March 20). Alder. Wikipedia. Retrieved May 8, 2023, from   <https://en.wikipedia.org/wiki/Alder>

2Puisis, E., & THOMPSON-ADOLF, J. (2022, October 3). 12 Species of Alder Trees for Your Yard. The Spruce. Retrieved May 8, 2023, from   <https://www.thespruce.com/alder-trees-and-shrubs-3269701>

3The Conservation Volunteers. (2023). How to identify Alder. Grow trees. Retrieved May 8, 2023, from   <https://treegrowing.tcv.org.uk/identify/alder>

4The Woodland Trust. (2023). Alder (Alnus glutinosa) – British Trees. Woodland Trust. Retrieved May 8, 2023, from   <https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/alder/>

5Treece, K. (2022, October 13). What Is a Pioneer Species? Definition and Examples. Treehugger. Retrieved May 8, 2023, from   <https://www.treehugger.com/what-is-a-pioneer-species-5089870>

6Wikipedia. (2023, January 31). Phytophthora alni. Wikipedia. Retrieved May 8, 2023, from   <https://en.wikipedia.org/wiki/Phytophthora_alni>

7Warner, D. (2009, August 17). Sharp increase in dying alder trees. Irish Examiner. Retrieved May 8, 2023, from   <https://www.irishexaminer.com/opinion/columnists/arid-20098816.html>

8Stephens, M. (2009, June 18). Alder (Alnus rubra): It’s Possible You’ve Overlooked This One. Woodworkers Source. Retrieved May 8, 2023, from   <https://www.woodworkerssource.com/blog/wood-conversations/alder-alnus-rubra-its-possible-youve-overlooked-this-one/>

9The Conservation Volunteers. (2023). Grow Alder Trees from Seed – it’s easy – A Guide from TCV. Grow trees. Retrieved May 8, 2023, from   <https://treegrowing.tcv.org.uk/grow/tree-recipes/alder>

10U.S. Geological Survey. (2018, August 2). Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams | U.S. Geological Survey. USGS.gov. Retrieved May 10, 2023, from   <https://www.usgs.gov/publications/riparian-defoliation-invasive-green-alder-sawfly-influences-terrestrial-prey-subsidies>

11American University of Beirut. (2023). Oriental Alder. AUB. Retrieved May 10, 2023, from   <https://www.aub.edu.lb/natureconservation/Pages/orientalalder.aspx>

12Varela, P. C., Martínez, R. C., Vázquez, M. J., & Casal, A. O. (2010, February). First Report of Phytophthora Rot on Alders Caused by Phytophthora alni subsp. alni in Spain. PubMed. Retrieved May 10, 2023, from   <https://pubmed.ncbi.nlm.nih.gov/30754290/>

13University of Florida. (2022, April 7). Biopesticides: Horticultural Oils. UF/IFAS Gardening Solutions. Retrieved May 10, 2023, from   <https://gardeningsolutions.ifas.ufl.edu/care/pests-and-diseases/pests/management/natural-pest-control-with-oils.html>

14Norman, C., & Kreye, M. (2020, September 24). How Forests Store Carbon. Penn State Extension. Retrieved May 10, 2023, from   <https://extension.psu.edu/how-forests-store-carbon>

15Oregon State University. (2023). Red Alder (Alnus rubra). Oregon Wood Innovation Center. Retrieved May 10, 2023, from   <https://wood.oregonstate.edu/red-alder-alnus-rubra>

16Annette Meyer. Pixabay. Retrieved from   <https://pixabay.com/images/id-4681232/>

17AnRo0002. Wikimedia. Retrieved from   <https://commons.wikimedia.org/wiki/File:20120904Alnus_glutinosa02.jpg>

18San Bernardino Nat’l Forest. Flickr. Retrieved from   <https://flickr.com/photos/135365655@N07/44757671762>

19Alnus glutinosa kz28 Photo by Krzysztof Ziarnek, Kenraiz / Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) . Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_glutinosa_kz28.jpg>

20Alnus rubra, Iceland Photo by Berserkur / Attribution-ShareAlike 4.0 International (CC BY-SA 4.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_rubra,_Iceland.jpg>

21Juodalksnis Gumbulis Photo by Vilensija / Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Juodalksnis_Gumbulis.JPG>

22Alnus viridis tree Bulgaria Photo by Georgi Kunev / Attribution 2.5 Generic (CC BY 2.5). Resized and Changed Format. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_viridis_tree_Bulgaria.jpg>

23AnRo0002. Wikimedia Commons. Retrieved from   <https://commons.wikimedia.org/wiki/File:20150813Alnus_incana4.jpg>

24Alnus cordata alder tree Photo by Peter O’Connor / Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0). Resized. From Flickr   <https://flic.kr/p/6Yv2Su>

25Alnus serrulata arboretum Breuil Photo by Aroche / Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_serrulata_arboretum_Breuil_2.jpg>

26Aliso – Cerezo (Alnus jorullensis – acuminata) Photo by Alejandro Bayer Tamayo / Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Aliso_-_Cerezo_(Alnus_jorullensis_-_acuminata)_-_Flickr_-_Alejandro_Bayer.jpg>

27Alnus nepalensis × nitida kz03 Photo by Krzysztof Ziarnek, Kenraiz / Attribution-ShareAlike 4.0 International (CC BY-SA 4.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_nepalensis_%C3%97_nitida_kz03.jpg>

28Alnus japonica 05 Photo by Σ64 Attribution 3.0 Unported (CC BY 3.0). Resized and Changed Format. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnus_japonica_05.jpg>

29Alnus rhombifolia San Gabriel River Photo by Mitch Barrie / Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0). Resized. From Flickr   <https://flic.kr/p/8bVNJv>

30Alnusorientalis-10-4-08-TitreyenGöl-13-00-E-MK-15756a Photo by Michael Kurz / Attribution-ShareAlike 3.0 Austria (CC BY-SA 3.0). Resized. From Wikimedia Commons   <https://commons.wikimedia.org/wiki/File:Alnusorientalis-10-4-08-TitreyenG%C3%B6l-13-00-E-MK-15756a.jpg>

31Robert H. Mohlenbrock. Wikimedia Commons. Retrieve from   <https://commons.wikimedia.org/wiki/File:Alnus_maritima_leaves_catkin.jpg>