(Obscure) Asian Maple Species

Dipteronia sinensis

We have many Acer species in the Flora Wonder Arboretum, and also a Dipteronia sinensis which is closely allied to Acer. In the trade they are referred to as “species maples,” meaning anything other than the common forms of A. palmatum, A. japonicum and A. shirasawanum. At the beginning of my career J.D. Vertrees, the noted maple author and guru, asked me if I was interested in the species maples, and I replied, “Not particularly.” He responded, “You will one day.” I felt the way I did because I recognized that my limited brain capacity would have a difficult time to absorb obscure species with very limited market potential. Besides, many of them didn't even look like “maples.” When I was economically on my feet – though never well off – I began to admire and collect species new to me, and I guess the old codger was right after all.

Acer griseum

I found that I could sell Acer griseum, the larger the better, and it was a profitable species for me. Now they are so plentiful that their price has declined, but I suppose that Englishman E.H. Wilson would be happy to know that the tree he introduced would become so popular and useful. It is commonly used as a street tree in many towns and cities in Oregon due to its ornamental qualities and because it is tough and durable in the landscape.

Acer triflorum

Acer mandshuricum

Acer mandshuricum

Acer maximowiczianum

Acer x 'Cinnamon Flake'

Because of my initial success with A. griseum I naturally moved into the realm of Acer triflorum, a northeast China native with whitish-gray bark that exfoliates in a different manner than A. griseum. You will find A. triflorum in snob gardens and arboreta, but seldom will you see it in a typical home landscape. Even more rare in the Trifoliata section is Acer mandshuricum, the Manchurian maple. Its bark is dark brown and rough, but not exfoliating like the previous two. My older specimen is one of my first maples to leaf out in spring and one of the earliest to display its wonderful orange-red autumn foliage. So I like A. mandshuricum, but my customers don't know it, or even want to know about it. The related Acer maximowiczianum is doomed because of its cumbersome name, non-exfoliating bark and eventual large size. The cross of A. max. with A. griseum has yielded A. x. 'Cinnamon Flake', and that is a novelty that I can sell a few each year.

Acer micranthum

Peter Gregory

Whether or not a species is included in the Flora Wonder Arboretum is solely up to me – if I admire or am interested in it, then it's in, and I don't care if I have a market for it or not. I'm not on a mission to convert anyone, but one species that I feel should be commercial, but it is not, is Acer micranthum. So-named for having small flowers, it blooms in May in pendant clusters. The seed that develops is the smallest in the Acer genus and they turn pinkish-red in autumn. A. micranthum is at least as hardy as A. palmatum, and the former forms a slow-growing small tree with dainty green leaves in summer, and brilliant red foliage in fall. It roots readily as soft wood cuttings in summer, or can be grafted on any species in the Macrantha section (such as A. davidii). I fell in love with A. micranthum when I saw a beautiful specimen in England's Westonbirt Arboretum* on a drizzly October day. It glowed red in the gloom and was further adorned with pink jewel-like fruits. It was my first visit to Westonbirt, and author and Maple Society President, Peter Gregory, led the tour. When we came to the A. micranthum Peter stopped and just stood there smiling with great affection, just as you do with a beautiful and interesting woman, letting the maple speak for herself.

*An excellent photo of the Westonbirt tree can be seen on page 198 of DeBeaulieu's book, An Illustrated Guide to Maples.

Acer pentaphyllum

Acer pentaphyllum

Joseph Rock

The rare Chinese species Acer pentaphyllum was introduced to cultivation by T.T. Yu in 1937 according to The Hillier Manual of Trees and Shrubs 2014. However in the DeBeaulieu An Illustrated Guide to Maples, credit of discovery is given to Joseph Rock in 1929. In 1978 Vertrees in Japanese Maples (1^st edition) says that “seeds were first collected by J. Rock (Rock #17819) in the Szechuan Province along the Yalung River....A plant from Rock's seed is growing at the Strybing Arboretum in San Francisco, California.* All plants in cultivation in the United States have originated from that tree.” That statement was probably true in 1978, but I know that it is no longer so.

*I tried to pay homage to the Strybing tree but was told by staff that it no longer existed.

Then I learned that one plant, presumably a seedling offspring from the original tree in America, could be seen at the Western Hills Rare Plant Nursery in Occidental, California. The nursery and garden used to be a destination for serious gardeners, having been founded by plantsmen Lester Hawkins and Marshall Olbrich in 1960. Since I struck out at the Strybing I drove to Occidental and found the nursery still in operation, but now run by an Englishwoman. I toured the grounds and found a lot of interesting plants, although I didn't find the old Acer pentaphyllum. However there were a number of them in small pots on a bench in the sales area. I asked the woman if they were grown from cuttings – which I was doing at the time – but she responded that they were seedlings. I said that I missed the mother tree, where is it? She pointed straight up – we were standing right under it! Its canopy was a broad umbrella-shape with the branches pruned up, so possibly I could have walked under it a hundred times before noticing the distinctive five narrow-lobed leaves. Fortunately the garden has been preserved since the nursery closed in 2010, and as the Western Hills Garden you can tour it on Tuesdays and Thursdays for $10 per person.

Acer pentaphyllum seed

I was prompted into rehashing the A. pentaphyllum story because yesterday I noticed seed on my largest specimen. The problem with the species is that it is too tender to grow outside in Oregon, and even though I have been growing it for over 30 years, once a tree reaches the top of the greenhouse I sell it to someone in California. My current specimen is about 12 years old, and its amazing vigor is due to being grafted on “red maple” rootstock, Acer rubrum. Years ago I planted this combination into the garden, and the following winter we experienced a low of 5 degrees F. By July I determined that the pentaphyllum was as dead as a doornail, although rubrum rootstock sprouted from the base. I was hopeful that the hardy rubrum would impart a hardy boost to the pentaphyllum top, but not so, or at least not enough. I would encourage the next owner of the Flora Wonder Arboretum – once I croak – to be a plantsman of means and immediately construct a two-storied conservatory to house the pentaphyllum.

Acer calcaratum

Acer calcaratum new growth in August

Another tender – and rare – Chinese species, Acer calcaratum, is also housed in the pentaphyllum's greenhouse, and it too nears the top. The species grows in low-land rainforests of Yunnan, Myanmar, Thailand and Vietnam. The specific name calcaratum is from calcarate, and that from Latin calcar meaning spurred. I've not noticed my tree in flower or in seed, so I'm not sure what part is “spurred.” certainly it's not the tri-lobed leaves which resemble an Acer buergerianum on steroids. The best part is the reddish new growth which my specimen showed off in spring, and is now showing off again. I foresee no market for A. calcaratum, but for fun I will try to graft it on another species – maybe A. pseudoplatanus.

Acer forrestii

I notice that DeBeaulieu doesn't list A. calcaratum, nor does he list A. forrestii, and the leaves of these two species resemble each other somewhat. His Illustrated Guide to Maples is sparse with synonyms, and without re-reading his entire book I don't know where he “lumps” the two species. Even though I can write a blog on obscure Asian maple species, I really don't know them that well myself. I have seen a number of maples in the Himalayan foothills, “foothills” meaning below 10,000' in altitude, and in spring they can be beautiful with reddish-to-chocolate-brown new growth. Since they generally aren't hardy in Oregon I never felt compelled to bring them home.

Acer oliverianum

Acer oliverianum was named by German botanist Ferdinand Albin Pax in 1889 to honor English botanist Daniel Oliver, an example where plant experts can overcome national differences in the pursuit of science. The Chinese species forms a strong-growing tree with a wide canopy at maturity. It looks like a vigorous form of Acer palmatum, and in fact A. oliverianum is in the Palmata section and is graft-compatible with A. palmatum. One Japanese nurseryman whispered a secret to me, even though he was alone with just me and my wife, that when using A. oliverianum as rootstock, the variegated cultivars of palmatum would produce more coloration. I doubt that he, or anyone in Japan, reads the Flora Wonder Blog, so what's the harm to now present his theory? I tried A. oliverianum myself as rootstock, but my variegates looked pretty much the same as with palmatum. After three years the cultivars were either sold or mixed in with the others so I can't report beyond that. One concern would be A. oliverianum's hardiness – more or less than palmatum? – and I suspect that coming from central China it would be less.

Acer pycnanthum

Acer pycnanthum is a Japanese species that is closely related to America's Acer rubrum. I used to assume that the specific epithet was a corrupt spelling of Latin pyra, which is from Greek pura for “hearth,” from pur for “fire.” That assumption was because A. pycnanthum, like A. rubrum, begins the spring with red flowers before leaves appear, then finishes in fall with blazing red foliage. But wrong – the name is derived from Latin pycnanthus for “having flowers in dense clusters.” The maple is somewhat rare, growing in a limited mountainous area of Nagano on Honshu Island. My girlfriend (at the time) Haruko was surprised but pleased that I had a specimen in the Arboretum, and perhaps that is why she agreed to marry me. She graduated from the University of Tokyo's landscape architecture department, and she remembers in her plant ID class that her favorite professor beamed with pride when he pointed out the only specimen of A. pycnanthum on campus. Haruko aced her class, then hurried to America for nuptial bliss.

Acer sieboldianum

Acer sieboldianum

Acer sieboldianum 'Kumoi nishiki'

Acer sieboldianum 'Sode no uchi'

Philipp von Siebold

Kusumoto Ine

Acer sieboldianum – I don't have the straight species in my collection, but a nice tree is growing at the nearby Rhododendron Species Garden in Washington state. “Siebold's maple” of course honors Philipp von Siebold, the German physician and botanist who introduced numerous flora of Japan into Europe, and who also kick-started the introduction of Western medicine into Japan. Naturally he was attracted to Japanese women and he married one; I can certainly relate to that. He fathered Kusumoto Ine who went on to become the first female Japanese doctor, then court physician to the Japanese Empress. Siebold's maple is compatible with Acer palmatum as rootstock, and I grow the cultivars 'Kumoi nishiki', 'Mikasa yama', 'Sode no uchi' and the spreading, semi-weeping 'Seki no kegon'. To the casual observer – and me too – A. sieboldianum resembles Acer palmatum, although I haven't studied the former's sexual expression. I agree with Hillier that sieboldianum is a “small tree or large shrub,” but then the comparison with Acer japonicum: “similar in ornamental merit...but with flowers yellow, not red...” seems to be a strange description since they look so different. Am I similar to a duck because we both have wide feet? Furthermore, M. Yano in Book for Maples lists the 'Sode no uchi' cultivar as belonging to the Acer tenuifolium species. Again, I don't know the Asian Acer species expertly; and if I did I would only end up arguing with other botanists, as they are a most contentious group. For example, DeBeaulieu doesn't even list tenuifolium as a species.

Acer pseudosieboldianum

In any case botanists should probably be outlawed from naming plants. The Japanese Acer sieboldianum was first described by Dutch botanist Miquel and then the German botanist Ferdinand Albin Pax in 1904 coined the specific name Acer pseudosieboldianum for the similar species from Korea, China and Manchuria. I really don't like pseudo for any botanic name because if it's really a separate entity then let it's name stand on its own and not be “like” or “false” something else. If a Pseudotsuga is not a true hemlock then don't allay its name to what is different. The worst plant name in horticulture is Acer japonicum 'Aconitifolium', rendered since its leaves resemble the Aconitum genus. The Japanese don't use the crappy Latin cultivar name, rather they prefer Maiku jaku or “dancing peacock.” Anyway A. pseudosieboldianum differs from A. sieboldianum because the former comes from a different locale (and is more winter hardy) and because the leaves are larger. Myself, I couldn't tell you the identity of an older A. sieboldianum, A. pseudosieboldianum, or even A. shirasawanum if asked to do so. In fact I have attended Maple Society events where the world's botanists squabble about the specific identity of a tree. I never take the bait and offer my opinion because it wouldn't be “valid” anyway. Frequently, so as not to come to blows, they throw up their arms and proclaim the tree to probably be a hybrid anyway...then move on to the next argument.

Acer pubipalmatum

Most of us maple collectors wouldn't know the difference between Acer palmatum and Acer pubipalmatum, and pubipalmatum at best would just seem to be a variety of palmatum. DeBeaulieu is a splitter in this case and gives pubipalmatum specific rank while Hillier doesn't mention the species at all. If you look closely you will see some minor differences, and indeed pubipalmatum has finely hairy leaves. Besides the pubescent leaves, pubipalmatum usually has seven lobes with the middle lobe a little longer and pointing sharply.* It is also a stronger grower and somewhat less dense than palmatum, and besides it is native to China, not Japan. One could say that this Chinese maple is less refined than the Japanese maple, and to be politically incorrect, my Japanese father-in-law would say the same about the people.

Acer pubipalmatum 'Flying Daggers'

*The cultivar Acer pubipalmatum 'Flying Daggers' has small leaves with more-narrow and pointed lobes than the type. A Mr. Maple selection from North Carolina.

Acer pauciflorum

Another palmatum look-alike is Acer pauciflorum, but it is not listed in either DeBeaulieu's or Hillier's book. My source for the “Few-Flowered maple” was Heritage Seedlings and it was offered in their 2013-2014 wholesale catalog. According to Heritage, “Almost unknown in the West, these are among the first of seedlings to be offered in the U.S. Closely related to Japanese maple, it is reported to be more drought and cold tolerant than A. palmatum....Try a few and join us in an extensive field trial.” Ok, I fell for the pitch and now I have some 7' healthy-looking green-leaved trees. I'll keep a few away from sales with the intention of rooting cuttings from them. If that goes well I'll use them as understock and conduct a trial to see if it does improve plants with “more drought and cold tolerance.” Or rather, I won't trial. To really do it right would take at least half a career, and I'm well on the downside of mine. Besides it would take input from other growers from around the country to determine if A. pauciflorum would make an improved rootstock. Hey young Man, why don't you do the trial?