Here’s a little mystery. Hibiscus hamabo is one of those odd woodies along the eastern coast of China that inhabits slight hammocks in the wetlands and salt marshes of the Yangtze river as it spills out of Jiangsu Province. The range runs down into Zhejiang Province until the purely tropical mangroves take over the place. If you want to learn a little more about this mysterious plant, there’s an interesting YouTube video here: https://www.youtube.com/watch?v=7-uCzawft3M
A little backstory: I have been collaborating with Professor Yin Yunlong of the Nanjing Botanical Garden, Nanjin, China, for many years and as part of that work, I’ve enjoyed being part of the coastal windbreak forest project of coastal China. This megaproject includes the planting of literally millions of trees on the inland sides of coastal dikes. Climate change is not a theory in China. It’s accepted science and the country is rushing to green the environment. With more solar added last year than the USA has added in our history, it’s not possible to avoid the conclusion that this country is attempting to move away from fossil fuels. Having surpassed the USA as the world’s largest emitter, the need is obvious. With 1.3 billion citizens, many lifted into the consumptive middle class, this is no easy chore. Switching from fossil fuels to geothermal, hydroelectric and solar takes a heavy investment and China is stepping up. With megacities like Beijing and Shanghai sitting right near sea level, the urgency is not lost on the scientific community. It long ago surprised me that professors, government officials, and every college student I’ve encountered in my China connection accept global warming and climate change as fact. After all, carbon dioxide and methane are increasing (no dispute there) and the science says that raises the temperature, so what’s the debate? If you go back in time, it’s happened before. It’s happening now. So, when I’m asked, as I often am, why so many in my country debate this fact, I always say, “it’s complicated.” Enough said.
Back to the Hamabo Hibiscus. We’ve had H. hamabo at SFA Gardens as a long ago acquisition from our good friend and personality, Bob McCartney, Woodlanders, Aiken, SC. Parked in the Arboretum several decades ago and never pruned, it’s grown into a robust bullet proof shrub, a gnarly spreading beast. While I liked it for its Texas tough nature, it’s never stood out as a showboat. With short lived yellow flowers in the summer and good Fall color, it’s nice but I suspect it won’t grace the aisles of Home Depot, Lowes or Walmart anytime soon.
In 2016, we kicked off a Moody Gardens research project to evaluate “climate change friendly” plants for a 21st century Galveston Island, Texas. Our mission is to evaluate not just the ornamental commodities of the island but to stretch the envelope to plants that have never been tested there before. Hibiscus hamabo was one of the latter. Planted in the Spring, 2016 as way too tiny plants, it’s done well. With soil and aerial salt challenges, it seems cheerful after the first season in the ground.
While in China in August 2016 I was visiting with Yin and learned that he had made two interesting observations with the plant. Like many of us, he sometimes fails to sleep well at night and is prone to take a walk on the streets of Nanjing near his apartment, perhaps grab a bowl of noodles from a shop, drink a cup of tea. Nanjing never goes to sleep. It’s not Nacogdoches. During one sojurn, he wondered if he could graft Hibiscus syriacus, Althaea or Rose of Sharon, on to H. hamabo and get it to take. He tried it. It worked. I saw the grafted plants, and, yes, the unions looked good and the althaea looked happy on top of the hamabo rootstock. What makes this significant is that this popular woody ornamental does rather poorly in salt affected soils. When I returned to the USA, even though it was a little late in the season for grafting, I tried a half dozen and they all took rather quickly.
The second observation came early in 2016. Professor Yin Yunlong who is a long time student of this plant, speculated the plant may use mycorrhiza to deal with the salt levels encountered by the plant. He has found “nodules” on the root system. My first thought after looking at the images was nematodes! However, Yin said a first microscopy suggested not – and it’s not a fungi, but a bacterium causing the anomaly. More investigations are underway. So, as part of the Moody Gardens research project, Dr. Josephine Taylor and Dr. Steve Wagner, both in Biology, and Steve’s graduate student Elaine Fowler are investigating this interesting plant at SFA and in the Moody Gardens research plots for possible associations with mycorrhiza that may have something to do with its salt tolerant disposition.
Finally, as you might expect among horticulturists, there has been some debate about whether we are actually working with the “true” H. hamabo. Conversations with Adam Black, Peckerwood Gardens, led to a newer acquisition that is morphologically quite different. Adam’s plant has larger leaves and more glabrous foliage than “our” hamabo and he noted that the flowers start off yellow but fade to orange rather quickly. That said, the plant provided by Adam does appear quite different to what I’ve observed along the coast of China. While yet to bloom for us, I think Adam’s plant is quite similar to H. tiliaceus, perhaps known as Talipariti tiliaceum, which can reach 40′ in height and can be damaged by cold in our region. Both are reported to be drought, salt and hurricane tolerant and both will be finding a home at our Moody Gardens project.
From the Flora of China, Volume 12, pages 287-288m Hibiscus hamabo is described as follows: Hibiscus hamabo Siebold & Zuccarini, Fl. Jap. 1: 176. 1841. 海滨木槿 hai bin mu jin. Synonyms: Hibiscus tiliaceus Linnaeus var. hamabo (Siebold & Zuccarini) Maximowicz; Talipariti hamabo (Siebold & Zuccarini) Fryxell. These are trees or shrubs, deciduous, 1-5 m tall, young stems softly stellate pubescent, stellate hairs 0.5 mm or less. Stipules foliaceous, oblong-ovate, ca. 1.5 × 1 cm, deciduous; petiole 1-2.5 cm; leaf blade orbicular to broadly obovate, not lobed, 3-6(-7) × 3.5-7(-8) cm, abaxially densely whitish puberulent, adaxially sparsely and minutely stellate pubescent, basal veins 5-7, base cordate, margin irregularly crenulate to subentire, apex abruptly acuminate; abaxial nectary at base of midrib. Flowers solitary, axillary, or by abortion or reduction of upper leaves in a few-flowered terminal raceme. Pedicel 3-10 mm, with densely mixed simple and stellate hairs, accrescent in fruit. Epicalyx cup-shaped, ca. 1 cm, lobes 8-10, connate for 1/2 of length, narrowly triangular. Calyx campanulate, 1.8-2.1 cm, deeply 5-lobed, longer than epicalyx; nectaries present, obscure. Corolla showy, yellow later turning orange-red, with dark red spots in center, 5-12 cm in diam.; petals obovate, 4-5 cm, stellate pubescent abaxially. Staminal column 1.5-2 cm, glabrous, apical 2/3 antheriferous, ca. 1/2 as long as petals. Style branches longer than staminal column; stigma capitate. Capsule ovoid, 2.5-3.5 cm, densely brownish hirsute. Seeds reniform, ca. 4.5 mm, minutely papillate (appearing glabrous). Coastal sands; near sea level. Zhejiang [Japan (Bonin and Ryukyu Islands), Korea; cultivated in India and Pacific islands (Hawaii)]. This species is easily recognized by its obovate leaf blades.
While there’s a nomenclature issue here, it’s possible that there’s a long historical misuse of the name hamabo. Adam wrote recently that, “I am only deferring to the late Malvaceae specialist Paul Fryxell’s determination, who personally identified the clone I gave you from Dolores Fugina and the late Richard Button of Bloomin’ Good Nursery in south FL. I wish Dr. Fryxell was still around to shed some light on this. Under his work, he segregates these (including H. tiliaceus) under the genus Talipariti. In fact, the “true” hamabo, whatever it is, was once listed as H. tiliaceus var. hamabo, lending more evidence that the true hamabo may look moer “tiliaceus-ish” than the other clone, which I think is quite different in foliage and form than all the “Talipariti” types. Still, I realize the other clone that is in more widespread cultivation in the US and throughout coastal Asia is widely called H. hamabo. Maybe Paul was wrong, or maybe it was one of those cases where a name on a universally known plant has been misapplied all along when compared with type specimens and original descriptions.