Written by s • Get to Know the Different Groups of Japanese Maples
Perhaps the most adored of all trees, Japanese maples have an aura around them – a flavor of the exotic, the special, and the desirable. For many gardeners they are their most valued plants, and while you might struggle to succeed with them in some parts of the country, generally they much are easier to grow – with a little basic care – than the reputation they have among some of being ‘hard to grow’. They aren’t in fact at all hard, as long as they have the right balance of light and shade, and of water and drainage in the soil. You can prune them, or leave them to grow as they wish – either way the result is a plant of enormous appeal, that grows more beautiful with every year it spends in your garden.
A Profusion of Varieties
One thing that any gardener starting out with them will see is that there are so many of them! Definitely there are more different varieties than of any other tree, and this certainly makes choosing difficult! Each variety has a name, and each one is different in many ways. Some may be upright, others mounding or weeping; the bark may be green, yellow or red; some grow quickly, others more slowly; and of course, and most importantly, the leaves are different in shape and color.
Although the most common and usual Japanese maple is the tree called Acer palmatum by botanists, that isn’t the only species found in Japan. For example, there is the full-moon maple, Acer shirasawanum, and also the plant called by the Japanese Acer amoenum, which in Western classification is seen as a sub-species of the Japanese maple, and called Acer palmatum subsp. amoenum. Another sub-species often called a species is Acer palmatum subsp. matsumurae. Another maple, Acer sieboldianum, also grows in Japan and is sometimes confused with, and sold as, Acer palmatum. Finally there is a maple from the northwest, the vine maple, Acer circanatum, which is also grown by lovers of the Japanese maple, to which it is related. All these trees are in a section of Acer called ‘Palmata’, because of the leaf divided like a hand.
Now for botanists, that is as far as they go, and they don’t pay attention to all those different leaf colors, tree shapes and other ‘details’. This is because botanists look mainly at the flowers of plants to decide what they are, while leaf shapes and other things – while still important – take second place. This is very different from gardeners, who really notice leaves, and tend to distinguish plants like Japanese maples based on leaf shape and color.
Now wouldn’t it be nice if when we gardeners looked at a list of Japanese maples, there was something more helpful than that cultivar name? That’s the one in single quotes, that sometimes says something descriptive, but often doesn’t. ( The word ‘cultivar’ is the correct name for what we gardeners usually call a ‘variety’, a word that already has another meaning to a botanist.)
So a cultivar name like ‘Orange Dream’ gives us some clue, but a name like ‘Koto Ito Komachi’ isn’t much help at all.
That isn’t just because it is obviously a Japanese name, either. If I tell you that it translates as ‘small 5-stringed harp’, does that help? Didn’t think so, but the connection is that the leaves are divided into narrow lobes, maybe as narrow as harp strings. It’s not an immediately obvious connection that most people would make.
Bringing Order out of Chaos
Well, nurseries too struggle with this issue, and they know that the tree-buying public would like some help in choosing, especially if the tree has no leaves when they are buying it, and maybe just a tiny picture on a tag. Here at the Tree Center we give you some nice big pictures, but even our page of Japanese Maple Trees can be a bit overwhelming the first time you look at it. And there is a second page as well. . .
So, some of the world’s top experts on these trees have put their heads together and developed a system for organizing all those different trees, using mainly leaf shapes, but other features as well – all things that any gardener can easily identify on a Japanese maple. This system has only been around since 2017, so it is still new, and hasn’t yet been widely adopted. But soon enough it will catch on, so we are going to present that system here, as a guide to what may soon show next to the full name of the tree you are looking at. It will immediately tell you something about the tree, even if it is just a list with no pictures, or a stick bare of leaves.
To get to the roots of this new system, we need to travel to the area around the town of Boskoop, in the Netherlands. For centuries Holland has been in the lead with horticulture, and supplies much of Europe with garden plants. So it’s natural they would take the lead in trying to improve things. If you are in Boskoop, and you love maples, then be sure to visit the Aceretum, or Maple Park, at Plantentuin Esveld, a large nursery that has been in existence since 1865. There you will see what is probably the world’s biggest collection of maple trees, with over 1,000 different species and cultivars. There are about 160 different species recognized by botanists, meaning the collection has almost 900 different cultivars, many of them Japanese maples. In charge is Cor van Gelderen, one of the top Japanese experts in Europe. He developed a grouping of Japanese maples based mainly on leaf form and color, and also on bark. His starting point was an earlier classification developed in 2010 by Benoit Choteau, a Belgian nurseryman who is also a major grower and top expert on Japanese maples.
The Cor van Gelderen Classification of Japanese Maples
Van Gelderen’s system was accepted by the chief Netherlands horticultural association, and in 2017 by the Maple Society, the main international non-profit group for lovers of Japanese and other maples. The goal of the system is to make it easier for labels to be understood by ordinary gardeners.
Like everything new this system is not without controversy, and many people have given it very little attention. We are waiting to see if the ‘big guys’ start using it, and then we might follow. So for now, this is given here out of interest, but also as an good way to point out the incredible diversity there is among Japanese maples. Each group has one cultivar that is the ‘type’, a clear example of what the leaf looks like, which is used for the picture.
Note that if a cultivar seems to fall into two groups, the exceptional characteristic is the group it belongs in. So a tree with deep serrated lobes (Group Dissetum) and also red leaves (Group Atropurpureum), would be considered as being in Group Dissectum, as that distinguishes it from others with red leaves that are more normal.
So here are the 17 groups in the Official Classification of Japanese Maple Cultivars.
Group 1 – Amoenum
This group are all cultivars that have non of the features that would put them into other groups – in other words, you could think of this as the ‘basic’ type, from which all others could be derived. The type cultivar is this lovely tree, just turning red for the fall, a brilliant color that is its main feature. Notice the relatively wide lobes, that don’t go all the way to the bottom of the leaf.
Group 2 – Atropurpureum
This group contains all cultivars that have red leaves throughout the summer. The exact leaf shape is not significant in this group. The type cultivar is the popular and well-known classic tree bred in America’s older nursery, the Bloodgood Nursery in Flushing, NY.
Group 3 – Aureum
Plants in this group have yellow or orange spring foliage, that turns yellow to lime-green or chartreuse in summer (often influenced by the amount of direct sunlight). An outstanding example is ‘Summer Gold’, a tree developed in Italy earlier this century.
Group 4 – Convexum
This is a small group of cultivars, all of them with a unique leaf-form. The leaf curves downwards on either side of the vein running down each lobe, giving it a curled-over look. Notice that the leaf shape feature is treated as more important than the red color, which can be seen in many different groups.
Group 5 – Corallinum
All the plants in this group are known for the special tones of pinks and light reds that the new leaves show in spring. They turn green for summer, and then usually have bright fall colors.
Group 6 – Crispum
These unique trees have ‘crisp’ leaves, that is, they are crunched up and crowded together. The Lion’s Head Maple (‘Shishigashira’) is the most well-known, and can grow to 10 feet. Most, though, are much smaller.
Group 7 – Dissectum
For many people this is the classic Japanese maple, with the lobes of the leaves cut right to the base, and double serrations along the edges of those thin lobes. Almost all are weeping, and there are many varieties, since this is a very coveted look. Not as easy to grow as many others, because the leaves dry out so quickly if there is any dryness at the roots. These plants are all probably descended from Acer palmatum subsp. matsumurae, which has similar deeply cut leaves. Sometimes called Laceleaf maples.
Group 8 – Linearilobum
Very narrow lobes cut to the base, with almost parallel sides, but not as deeply serrated as in Group 7. The type cultivar is also one of the most popular of these trees, ‘Koto no ito’. Another beautiful variety is ‘Atrolineare’, where the leaves are also red. Notice that ‘Atrolineare’ does not, therefore, belong in Group Atropurpureum.
Group 9 – Matsumurae
Like the plants in the Dissectum Group, trees in this group are all derived from Acer palmatum subsp. matsumurae, but they are closer to it. Their leaves are divided to the base, with 7 or 9 lobes, but they are not as slender, and serrated in a more basic way, lacking the lacy look of Group Dissectum.
Group 10 – Marginatum
These cultivars have variegated leaves that have a distinctly-different coloring along the edges, such as white edges on a green leaf. When growing plants of this type, be careful to remove any plain-green stems that might sprout – it occasionally happens – because these will be more vigorous, and soon overwhelmed the variegated branches. The white edges often turn pink in fall, as shown here.
Group 11 – Palmatum
These trees have leaves divided about two-thirds of the way to the base, no more, with 5 or 7 lobes, and without any exaggerated features like lacy edges. They are closer to the wild tree, but more refined, and are often vigorous, growing into large specimens. The type cultivar, ‘Diana’, is here shown in its fall colors.
Group 12 – Pinebark
In this group it is the bark that is distinctive. Unlike most Japanese maples, whose bark is mostly smooth, these plants, even when young, develop thick, corky and deeply furrowed bark. The trunks do indeed look like a pine tree.
Group 13 – Redwood
Again, in the group, it is the bark that is the feature, but this time it is the younger twigs, that are bright red or orange. The color develops best as trees grow older, and are in plenty of sun. The famous Coral Bark Maple, ‘Sango-kaku’, is an outstanding example of this group.
Group 14 – Reticulatum
These plants have leaves with very pronounced veins in a different color to the background of the leaf. This produces striking patterning, especially in spring and fall when the leaves are colored. ‘Nathan’ is the type cultivar, but ‘Jubilee’ shows the reticulate patterning even more.
Group 15 – Sessilifolium
This rare group has leaves with no petiole – the leaf stalk. So the leaves sit right on the stem, looking like a cluster of separate single leaves, and giving these trees a very distinctive look.
Group 16 – Variegatum
This group covers all forms of variegation found that isn’t a distinct, contrasting border as seen in Group Marginatum. So there is a wide range of leaf patterning in this group. The type cultivar is an old variety from Japan called ‘Uki-gumo’. ‘Sagara nishiki’ is very different, but also belongs in the Variegatum Group.
Group 17 – Witches Broom
A witches broom is a group of branches much smaller, with smaller leaves, that develops on an existing tree. It is often the result of a non-lethal virus. In Japanese maples this almost always makes the central lobe of the leaf shorter than the next pair, so that’s a sure-fire way to tell the plant is a witches broom and not an ordinary dwarf variety. Notice that in this picture of the type cultivar.
That’s All Folks!
That brings us to the end of this survey of the new classification system. Hopefully we will start to see it in use – see how it helps organize the vast number of varieties into clear groups? If you want to decide what group a tree you already have, or see, belongs in, this useful key from the Maple Society is a great help, and saves you scanning over all the groups every time.
