Maple Species from Japan (Part 1)

Acer palmatum

Acer japonicum

Acer shirasawanum

The islands of Japan are blessed with a sizable number (about 20) of Acer (maple) species, some of which you have probably never seen. Most growers, both commercial and the hobbyist, are quite familiar with the Big Three: with Acer palmatum certainly, and to a lesser extent Acer japonicum and Acer shirasawanum. All three are compatible (as rootstock-to-scions) with each other, although there are other species that would combine as well (for example the Chinese Acer oliverianum).

Maple grafts

Early in my career I collected and propagated cultivars (cultivated variants), and I assumed at the time that the three species were sufficient to cover what ever was to be the future of Buchholz Nursery. The late maple guru and author, J.D. Vertrees, took an interest in my company, which pleased me greatly. Once he asked if I was interested in other species of maple, to which I replied, “Not particularly.” He responded, “Well, you will.” Vertrees wasn't aware, apparently, that my mental faculties were at their limit with just three species, and I blamed the “full sponge theory” for my limitations, that my brain couldn't absorb any more information without deleting some of what I had already processed. Besides, I was obsessed with money...because I didn't have any, and all of my efforts were geared toward financial survival. Well, Vertrees was right and I eventually began to study and propagate other species, to my great enjoyment. But I was right too, in the sense that the Big Three have accounted for over 95% of my career's maple sales.

Carl Peter Thunberg

Thunberg's Flora Japonica

The great botanist Linnaeus coined the genus name of Acer which is Latin for “sharp,” apparently in reference to the sharply pointed lobes on some species. A student, or “disciple” of Linnaeus was Carl Peter Thunberg (1743-1828), a Swedish naturalist who eventually traveled to Japan and produced his Flora Japonica in 1784. His sojourns were limited but he was the first to describe Acer palmatum in 1820, a species also found growing in eastern China, Korea and Taiwan. Acer japonicum followed in 1864, although Thunberg was long gone by then.

Gen ichi Koidzumi

Peter Gregory admiring an Acer circinatum witches broom
 at Portland, Oregon's Hoyt Arboretum

If you investigate the history of the last (of these three) specific epithets, credit for Acer shirasawanum goes to “Koidz,” who describes the species as, “A small bushy tree or large shrub of elegant habit...” Since I have propagated and sold many thousands of these “bushy trees,” I'm naturally curious to know about the specific namer. Gen ichi Koidzumi (1883-1953) was a Japanese botanist who specialized in the Rosaceae family besides maples, and who could argue for a better, though unrelated, combination? He was Professor of Plant Taxonomy at Kyoto University and helped to found the journal Acta Phytotaxonomica et Geobotanica in 1932, and also worked on the Revisio Aceracearum Japonicarum in 1913. With fellow botanist Takenoshin Nakai he compiled Trees and Shrubs Indigenous in Japan Proper in 1927. Though the intellectual held university credentials, I wonder what he was really like in the garden or field. Some of these “professors” are/were insufferable and amateurs such as I have learned to give them wide berth. Others have dirt under their fingernails and are primarily motivated by instilling enthusiasm for botany with children and the rustic layman. I fall somewhere between these two groups, and I recognize and appreciate the efforts of Acer experts such as the late Englishman Peter Gregory, author of Japanese Maples (4^th edition), as a down-to-earth apostle for the Acer genus.

Acer pictum 'Hoshi yadori'

Acer pictum 'Usu gumo'

When Vertrees quizzed me about additional Acer species, at the time we were standing near Acer pictum 'Hoshi yadori', a large-leafed species of A. pictum, and a cultivar with cream-white splashed or dotted (sunago fu) on the green bat-wing-like green leaves. Honestly I didn't care for any of it at the time and I still don't. Acer pictum 'Usu gumo' is more my type, and it's a colorful, compact variegated selection that has never been difficult to sell. Usu is Japanese for “thin” and gumo means “spider” or “cloud.” With the maple in question, “thin cloud” seems an appropriate name, however the network of veins on the leaf resembles a spider-web pattern.

Acer pictum 'Usu gumo'

Acer pictum 'Usu gumo'

Vertrees describes 'Usu gumo' as “difficult to propagate and not widely known in collections.” I've done my part to make it available, using Acer truncatum as rootstock, and I consider it as “easy” to graft as any maple cultivar if one begins with healthy rootstock and young, vigorous scions – the type that you'll find on five-year-old plants grown in containers that are pushed in a protective greenhouse. I don't want to come across as dismissive (or sacrilegious) about the Vertrees experience, but I regret that we didn't have more time together to share our propagation experiences.

Map of Sakhalin Island

Ainu people of Japan

Acer truncatum

Acer truncatum

Acer truncatum (“Shantung maple”) is occasionally grouped with “Japanese maples” because the Chinese native is closely related to Acer pictum, and because it occurs on Sakhalin Island which is located just north of Hokkaido, Japan, a territory that Russia currently controls through its military power, but a land that contains remnants of the pre-Japanese native Ainu people, and was first settled by Japanese fishermen on its southern coast. Acer truncatum is a tough, hardy, small deciduous tree that is championed by Metro Maples Nursery in Fort Worth, Texas where it performs admirably in that hell-hole environment. The species was named by Alexander von Bunge (1803-1890) (of Pinus bungeana fame) who was actually born in Kiev, Ukraine, which likewise the Russians now claim to own.

Acer buergerianum

Acer buergerianum 'Mino yatsubusa'

Acer buergerianum subsp. ningpoense

Acer buergerianum subsp. ningpoense

Acer buergerianum (“Trident maple”) is another Chinese species that many assume to be a Japanese native, but only because it is widely cultivated in the “Land of the Rising Sun.” The cumbersome specific epithet honors J. Buerger (1804-1858) who discovered the maple, but it's far easier to call it the “Trident maple” due to its normal appearance with three lobes. There's no maple species, in my experience, that out-shines the Trident for fall color, and with the dwarf cultivar 'Mino yatsubusa' you get green, yellow, orange, red and purple, often at the same time. A subspecies of Acer buergerianum is ningpoense, coming from Ningpo (or today, Ningbo), an area in Zhejiang, China. It is probably a zone less cold tolerant (to USDA zone 6, -10 F) than other locations of the Trident. De Beaulieu throws me into some confusion when he describes the leaves of the subspecies as being “two-lobed,” when the photos above clearly demonstrate three lobes. Furthermore, De B states that “On the young shoots the red leaves are in groups of three, with a larger leaf in the middle...” I've not seen any such grouping, so I'm left to wonder if my version is accurate. This is where the Flora Wonder Blog should become a two-way street, a forum, so I would appreciate if someone could set me straight, thanks.

Philipp von Siebold

Siebold's Flora Japonica

Philipp von Siebold (1796-1866) is no stranger to the Flora Wonder Blog, and the German physician/botanist was known for his studies of the Japanese flora and fauna. A maple was named in his honor, Acer sieboldianum, by botanist FAW Miquel. Siebold also penned a Flora Japonica, as did Thunberg earlier, with the help of another German botanist, Joseph Gerhard Zuccarini (1797-1848). The work appeared in 1835 but it was not completed in Siebold's lifetime, and after his death it was completed by Miquel.

Acer sieboldianum 'Sode no uchi'

Acer tenuifolium 'Keikan zan'

My experience with Acer sieboldianum is limited, and I have never grown the straight species, only a few cultivars. The first I collected was 'Sode no uchi', a slow-growing compact form. However, Japanese author Masayoshi Yano in his Book for Maples suspects that it more correctly belongs to Acer tenuifolium. The latter is difficult to find in the literature, and not as a recognized species, but as a variety (var.) of Acer shirasawanum, at least according to De Beaulieu in his An Illustrated Guide to Maples (Timber Press, 2003). I know of only one other cultivar of A. tenuifolium, 'Keikan zan', which certainly looks like a smaller-leaved version of the “Full Moon maple,” Acer shirasawanum. The reader probably grows weary at this point, and must wonder why any of this matters, to which I have no answer.

Acer sieboldianum 'Mequel'

Acer sieboldianum 'Kumoi nishiki'

Acer sieboldianum 'Mikasa nishiki'

The recognized cultivars of A. sieboldianum that I have grown include the wonderfully variegated 'Kumoi nishiki', 'Microphyllum' with smallish leaves, 'Mikasa yama' with its narrow canopy (at least for me) and the spreading, semi-weeping 'Seki no kegon'. I have also seen a variegated selection in Yano's collection, 'Mikasa nishiki', which was colorful in a pot in semi-shade. Another sieboldianum cultivar growing at Yano's is 'Mequel', but that was seen in late fall, with only one vigorous whip-shoot still with leaves; the only reason I mention 'Mequel is because I wonder if that is a misspelling of Miquel, the German botanist who finished Siebold's Flora Japonica. Hmm...

Acer pseudosieboldianum

Acer pseudosieboldianum

Specific epithets are given to plants to document particular attributes, such as alpina for those growing in alpine regions, alba for white colour, thunbergii to commemorate a plantsman/botanist, nana for a dwarf habit etc. I dislike epithets that allude to other plants, such as with Acer pseudosieboldianum, which would means the “false” Acer sieboldianum. I don't know – it just seems like the naming botanist took a cheap shortcut. Acer sieboldianum was introduced to the West in about 1880, while the similar Acer pseudosieboldianum was named by botanist Pax in 1904. Stuff like that can be confusing to the amateur gardener, if not the professional grower also. Come up with something original or leave the naming to another. In any case Hillier in Manual of Trees and Shrubs (2019) describes Acer pseudosieboldianum as “a very graceful, large shrub or small tree of spreading habit...” My experience differs, for those I have grown are usually narrow and straggly, kind of like our native “Vine maple,” Acer circinatum, and where growing in clumps is the best method to deal with the unshapeliness. Mark Krautmann of Heritage Seedlings, Oregon, has grown thousands of seedlings of A. pseudosieboldianum, commonly known as the “Korean maple,” and he describes it as a “wild species” that hasn't been grown long enough to settle into horticulture. Anyway, that's what he said 10 years ago, even though I don't quite follow that logic. The outstanding feature in my opinion is the vibrant autumn colours and a very important attribute is that the species is cold hardy to -30 F, USDA zone 4. The hardiness has been promoted in recent years with selections crossed with Acer palmatum, and I've seen the hybrids thriving in cold places such as in northern Montana, where the premier garden center in Kalispell carried no A. palmatums at all, only the hardy hybrids.

Acer carpinifolium

Acer carpinifolium

Acer carpinifolium 'Esveld Select'

Another Japanese species that alludes to a different plant is Acer carpinifolium, the “Hornbeam maple.” This small-to-medium-size tree was introduced from Japan in 1879 by Charles Maries who collected for the English Veitch Nursery firm. I've heard comments like, “That sure doesn't look like a maple to me!,” to which I love to point out a branch with the tell-tale maple samaras. Acer carpinifolium is also hardy to -30 F, or so they say – but I would sooner jump off the bridge than experience temperatures that cold in my Oregon nursery. I have only one specimen left at Flora Farm, but prior to that I grew a couple hundred seedlings which I found difficult to sell. I suppose because the flowers are insignificant and the autumn colour is yellow-to-brown, a subtle and warm, but uncommercial colour. One regret of my career is that I was never able to acquire the boldly serrated selection, Acer carpinifolium 'Esveld Select', discovered and named by the renowned maple nursery in Boskoop, Holland. Someone, please, treat me to a surprise!

Acer crataegifolium 'Eiga nishiki'

Acer crataegifolium 'Meuri ofu'

Acer crataegifolium 'Meuri ofu'

Acer crataegifolium 'Veitchii'

Acer crataegifolium 'Veitchii'

Yet another allusive specific epithet belongs to Acer crataegifolium, the “Hawthorne maple.” It too was collected by Charles Maries from Japan in 1879. Crataegus leaves are without much merit in my opinion, but the maple leaves of the Acer species don't resemble any Hawthorne species that I've ever seen anyway. What a shame to be saddled with a difficult name to pronounce and spell, especially since the maple is daintily attractive to me. There are a few variegated cultivars that I have propagated – 'Eiga nishiki', 'Meuri ofu' and 'Veitchii', with the latter two looking similar. What I find interesting is that the species was introduced in 1879, while the cultivar 'Veitchii' was introduced just two years later in 1881. Of course the “Veitch” name was chosen to honor the sponsoring English firm that sent Maries to Japan in the first place. I doubt that in just two years a variegated form could have been selected in England, and so the variegated clone must have been of Japanese origin. Did Maries discover it, or was there a Japanese grower who should get the credit? Did Veitch in England receive the one and only seedling specimen, or were there others in production? Hillier describes 'Veichii': “Leaves heavily mottled with white and pink, brilliant pink and purple in autumn.” One can produce 'Veitchii' from softwood cuttings in summer under mist, but for a stronger-growing tree the use of Acer davidii, or another species in the Macrantha section, is recommended. Brian Humphrey in his The Benchgrafter's Handbook (CRC Press, 2019) mentions that “Acer palmatum is also said to produce a compatible union.” I wonder about that comment since it seems unlikely to this nurseryman, but for the sake of the narrative we grafted a flat of 25 yesterday and I'll report my results in a year or two.

Acer crataegifolium 'Veitchii'

Masayoshi yano

I had an interesting occurrence with the aforementioned A.c. 'Veitchii', that an older specimen – always heavily variegated – was transplanted from the nursery to Flora Farm. Some digging trauma for a ball-and-burlap tree is normal, but usually it's a minor set-back and the victim will recover in a year or two. My specimen survived, but in spring it leafed out with just green leaves and no variegation. Then a 2^nd and 3^rd year passed, also without variegation. The famous Japanese maple guy, Masayoshi Yano, approached my tree with curiosity. After eyeing the tree he noticed the label and his face registered complete confusion. Why was there a 'Veitchii' with no colour? I recounted the digging-trauma theory but he still looked dubious, and to this day I imagine he viewed my credentials with suspicion. But in the 4^th spring after the transplantment the foliage emerged heavily variegated again, and I wanted to drag Yano back to Oregon to prove that my tree was indeed correctly identified. So: 3 years with no colourful variegation, the 4^th with spectacular colour...but the 5^th year nothing leafed out because the tree was dead. I felt that 'Veitchii' was ungrateful after all my perserverance. All of that was 10 years ago and I've been unable to source a replacement.

Acer micranthum

Acer micranthum

Acer micranthum from Westonbirt Arboretum

One of my favorite of all Japanese maple species is Acer micranthum, commonly called the “small-flowered maple” as the epithet micranthus means “having small flowers.” As with Acer crataegifolium, Acer micranthum can be rooted by cuttings, or by grafting on anything in the section Micrantha. A beautiful photo of the wonderful Acer micranthum in autumn (at Westonbirt Arboretum in England) is found on page 198 in De Beaulieu's illustrated guide, and in fact that's the very tree that got me hooked on the species. I was with Peter Gregory who was then head of the arboretum, and I remember his eyes sparkling with delight as he showed off its pinkish-red seed clusters. In spring the small pale-yellow flowers develop into tiny seeds, the smallest in the Acer genus. Everything about the tree is dainty, yet it is supposedly cold hardy to -20 F, USDA zone 5. I have grown it in full sun, the only problem being a slightly burnt trunk when the tree was young and the summer temperature exceeded 100 F. Acer micranthum was introduced to Europe about 1880, although it was described by Siebold and Zuccarini in 1845.

I'll pause for now, about halfway through my Maple Species from Japan, and hopefully I can continue next week with a review of other wonderful species.