Drought Tolerant Plants: Yellowhorn

A drought tolerant garden doesn’t have to be treeless. While the pickings are slim, there is a selection of trees that, once established, are well adapted to deal with extended bouts of little to no water. One such tree is yellowhorn, a species that demands to be considered for any waterwise landscape. Yellowhorn is rare in cultivation – and also restricted in its natural distribution – but perhaps that will change as word gets around about this beautiful and resilient tree.

Xanthoceras sorbifolium is native to several provinces in northern China and has been cultivated in a number of places outside of China since at least the 1800’s. Its ethnobotanical value is well understood in China. Its leaves, flowers, and seeds are edible and medicinal, and the high oil content of its seeds make them useful for the production of biofuels. Researchers are also investigating the use of yellowhorn for ecological restoration in arid habitats where desertification is a concern.

yellowhorn in bloom

Yellowhorn is the only species in the genus Xanthoceras, but is one in a long list of trees and shrubs in the Sapindaceae family – a family that now includes maples and horse chestnuts. It is considered both a large shrub and a small, multi-stemmed tree. It reaches a maximum height of about 25 feet, but arrives there at a relatively slow pace. It tolerates a variety of soil types, but like most other drought tolerant plants, it prefers soils that don’t become waterlogged easily. Its leaves are long, glossy green, and compound, consisting of 9 – 17 leaflets. The leaves persist late into the year and turn yellow in the fall. However, late spring, when the tree is covered in flowers, is when this tree puts on its real show.

Large white flowers with yellow-green centers that turn maroon or red-orange as they age are produced on racemes at the ends of branches. Small, yellow, hornlike appendages between each of the five petals of the flowers are what gives the tree its common name. Flowering lasts for a couple weeks, after which fruits form, which are about 2.5 inches wide, tough, leathery, and somewhat pear shaped. In my experience, most of the fruits are eaten by squirrels long before they get a chance to reach maturity. The ones the squirrels don’t get will persist on the tree, harden, and eventually split open to reveal several large, dark, round seeds nestled in chambers within the fruit.

To truly appreciate this tree, it must be seen in person, especially in bloom. At that point you will demand to have one (or more) in your garden. The seeds are said to be delicious, so you should give them a try if you can beat the squirrels to them. For a more thorough overview of yellowhorn, check out this article from Temperate Climate Permaculture, and for more photos of yellowhorn in bloom, check out this post from Rotary Botanical Gardens.

Squirrel nesting in yellowhorn, getting ready to go after more fruits.

All photos in this post were taken at Idaho Botanical Garden in Boise, Idaho.

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More Drought Tolerant Plants Posts:

Famous Botanists in History: Zhan Wang

Researching last week’s post reminded me of a series of posts that I have been wanting to start for quite a while: Famous Botanists in History. With Metasequoia on my mind, who better to inaugurate this new series than Zhan Wang – the botanist who made the first scientific collection of the living fossil.

From what I can tell, most of what is known about Zhan Wang (at least outside of China) comes from his contribution to the discovery and description of Metasequoia glyptostroboides, and even that information seems to be available largely due to the efforts of some of his colleagues and former students who endeavored to see that Wang be acknowledged for his role in the event. After Wang’s death, a group of his former students wrote a short biography which appeared in the August 2000 issue of the journal Taxon. The biography is written from the perspective of a group of people who greatly admired and respected their teacher and mentor. Unable to find much else written about Wang and his life, the details in this post are mostly taken from that biography. If there are other resources, I would be grateful to have them brought to my attention.

Zhan Wang was born in a remote village in Liaotung Province (now Liaoning Province) in northeast China on May 4, 1911. His birth name was Yishi, but he changed it to Zhan (or Chan) after running away from home in 1932. He developed plant identification skills early in his youth and used those skills to learn about Chinese medicine. He studied forestry in high school. When he graduated in 1931, the Japanese army was in the process of invading northeast China, so he fled to Beijing. There he continued his forestry studies at Beijing University (known today as Peking University). He graduated in 1936, and around that time, Beijing University along with other educational institutions and government agencies in Beijing and Nanjing were evacuating to escape aerial attacks. As Kyna Rubin puts it in The Metasequoia Mystery, “much of Wang’s early career was spent dodging war.”

Zhan Wang went to middle school and high school in Dandong City, Liaoning Province (photo credit: wikimedia commons)

Zhan Wang went to middle school and high school in Dandong City, Liaoning Province, China (photo credit: wikimedia commons)

Zhan moved with Beijing University’s Agricultural College to the Shaanxi province where he took a position as professor of dendrology and forestry. Wang’s students say that he preferred to teach his classes outside where the students could have “hands-on experiences” directly observing the morphology and ecology of plants. He “told stories about the species,” encouraged “looking, touching, tasting, and chewing,” and found many other ways to integrate botany and ecology in his courses. One way he helped students understand plant ecology was by grouping plants into categories with clever nicknames such as “mountain climbers” (plants found in cool climates), “greedy boys” (plants with high nutrient demands), “thirsty guys” (plants with high water demands), and “desert fighters” (drought tolerant plants).

In 1943, Wang became a Forest Administrator for the Ministry of Agriculture and Forestry, a position which included doing forest surveys in remote areas. On an expedition to Shennongjia in the Hubei province, Wang was stricken with malaria and had to stop in Wanxian County. There he met an old classmate of his, Longxing Yang, who told him of an unusual tree, which was later described as Metasequoia glyptostroboides by Wanjun Zheng and Xiansu Hu thanks to the initial collections that Wang made in July 1943. Despite being left out of some of the accounts of the discovery, Wang’s students claim that he didn’t complain and was more concerned about the tree’s continued survival, believing that “discussing the past discovery of a new species is not as important as investigating how a living fossil species will survive in the future.” His students were admonished to “focus on the species’ protection and its habitat.”

Wang’s position as Forest Administrator was short-lived; however, over the next several decades he continued to teach dendrology and forestry at several Chinese universities. Much of his research efforts were focused on sorting out the taxonomy of the willow family (Salicaceae), a highly complex plant family. He collected willow species throughout China and, with the help of his colleagues, described more than 90 new species. He also became very concerned about deforestation and “focused his attention on devising scientifically sound harvesting methods and successful regeneration processes.” Despite his work being largely restricted to China and (as his students claim) “receiving little credit elsewhere,” similar approaches to the sustainable forestry methods that Wang preached are “widely recommended and accepted today in western forestry practices for ecosystem management.”

Zhan Wang described many new species of Salix. Salix wangiana var. tibetica is a species that was described by and also named after Wang (photo credit: Flora Republicae Popuaris Sinacea)

Zhan Wang helped describe dozens of species of Salix that were new to science. Salix wangiana var. tibetica is a species that was described by and also appears to be named after Wang (photo credit: Flora Republicae Popularis Sinacea)

In the 1950’s, Wang began carrying out research at Changbai Mountain Nature Reserve high on the Changbai Mountain located in northeastern China on the border with North Korea. His efforts were interupted by the Cultural Revolution, a period that lasted from 1966-1976. As soon as that had passed, Wang and colleagues began working to establish the Changbai Mountain Forest Ecosystem Research Station. Wang became the first director of the station when it was approved and funded in 1979. Wang and his research team worked to establish “baseline information on the area’s flora, fauna, vegetation, and soils,” and in three years time had amassed enough research to warrant over 100 published papers. Due to the efforts of Wang and his team, the Changbai Mountain Nature Reserve gained inclusion in UNESCO’s Man and the Biosphere Program.

Wang’s students write that Wang viewed “Changbai Mountain as his home” and “believed that his life belonged to this mountain region.” His wish was to one day have his ashes “spread throughout the wilderness” of this mountain. After his death on January 30, 2000, his wish was carried out. “He will forever be with his beloved plants and forests in this important site of plant diversity, and now, place of rest.” Wang was survived by his three daughters; his son committed suicide during the Cultural Revolution, and his wife died in 1992.

In the adoring words of his students, Wang had a “kind, gentle character and contagious enthusiasm for science and nature” and “his contribution to botany went far beyond what is available in print. His footprints from exploring plants in China can be found in almost every province.”

The Discovery of a Living Fossil

In the early 1940’s, the genus Metasequoia was only known scientifically in fossil form. It had, in its day, been a widespread genus, found commonly in many areas across the Northern Hemisphere. It thrived among the dinosaurs. However, sometime during the Pliocene, the genus was thought to have died out. Thousands of fossils were left behind, and that would have been the end of the story had a member of its genus not been discovered still alive in a Chinese province later that decade. Its discovery is easily one of the greatest botanical stories of the 20th century, fascinating in its own right. The circumstances surrounding its scientific description, as it turns out, are equally interesting.

In the January 2016 issue of Landscape Architecture Magazine, Kyna Rubin details the event in an article entitled The Metasequoia Mystery. It’s the type of story that you almost need a crazy wall to sort out. A broad cast of characters interacted at various levels in order to make this profound discovery during a tumultuous time when the world was at war and China was being invaded by Japan.

Speaking of Japan, let’s start there. In 1941, Japanese paleobotanist, Shigeru Miki, published research describing fossils that for decades were thought to be either Sequoia or Taxodium as a new genus, Metasequoia. As Rubin points out, due to the war, “not every Chinese botanist would have had access to recent international research, let alone articles by botanists of an enemy country.” This could explain why in 1943 when Zhan Wang – a professer of forestry at Beijing University and the forest administrator for the Ministry of Agriculture and Forestry – was introduced to a living Metasequoia by an old classmate and local villagers in the Hubei Province, he wasn’t sure what he was looking at.

The tree was obviously important to the local people. They called it shuisa (water fir) and had built a shrine around it. Wang collected several branches and some cones that had fallen on a rooftop. At the time he identified it as Glyptostrobus pensilis (water pine), a tree common to the area; but he may have wondered if this was correct.

Eventually Wang’s samples and the details of his collection were brought to the attention of Wanjun Zheng, a dendrologist at the National Central University. Intrigued, Zheng sent his graduate student, Jiru Xue, to collect more samples from the same tree that Wang had encountered. These samples were more complete, and when they were presented to Xiansu Hu – the director of Fan Memorial Institute of Biology in Beijing – the mystery was solved. Hu had access to Miki’s research and concluded that what they had was a living fossil.

In 1948, Hu and Zheng published a paper describing the species and giving it the official name, Metasequoia glyptostroboides. The discovery ignited the botanical community as well as the general public, and soon seeds of what became commonly known as dawn redwood were being disseminated across the globe. Unfortunately, Wang’s contribution was not mentioned in the original paper, and the exact account of the discovery became convoluted.

photo credit: wikimedia commons

Dawn redwood (Metasequoia glytostroboides) is a deciduous, medium to large tree. Its cones are round and about 1 inch long. Its leaves are oppositely arranged and have a feather-like appearance. Its bark is fibrous, stringy, and red-brown to gray in color.  (photo credit: wikimedia commons)

At some point, a discussion between Zheng and a forester named Duo Gan (also known as Toh Kan) revealed that Gan had come across the tree in 1941, but he did not make any collections. Despite Zheng learning of Gan’s encounter after Zheng and Hu’s original paper had been published, Gan’s story became prominent, further obscuring the role that Wang played.

It’s important to note that none of Wang’s original collections were used as the type specimen – the particular specimen of an organism to which the scientific name is formally attached and is referred to in the scientific literature. The type specimen was collected by Xue. This is not uncommon, as initial collections may not always be in the best condition and may not include all the parts and pieces necessary to identify and describe a new species. But, as Rubin notes, “it was Wang’s specimens [that Zheng and others] had first examined and those specimens brought the tree to their attention to begin with.” So Wang’s contribution is an important part of the story.

Thanks to Wang’s former students, his role in the discovery has received greater exposure. Jinshuang Ma in particular has made it his mission to highlight the part that Wang played in the event. Apart from maintaining a website all about Metasequoia, Ma also spent several years searching for a lost herbarium specimen collected by Wang, which he found in an abandoned herbarium in Nanjing. You can read about his find in this article from the August 2003 issue of the journal Taxon. (Ma’s well researched summary of the events surrounding the Metasequoia discovery is also worth reading.)

Failure to acknowledge Wang’s contribution (at least initially) perhaps didn’t make waves outside of China, but in Rubin’s words, “the omission of Wang’s contribution sparked immediate hullabaloo inside China’s botanical circles in the late 1940’s.” Power and class differences likely played a big role. Hu and Zheng were established scholars that had received their educations in the United States and France respectively. Wang was young, from a remote village, and had not studied abroad. While Wang “went on to become one of China’s most distinguished forestry experts and botanists,” he was early in his career at the time of the Metasequoia discovery.

A deep respect for the elders in his field may be the reason that Wang’s students claim that he “never complained” about his treatment. His students go on to say that Wang “was not interested in personal gain,” and instead was simply satisfied to see that Metasequoia “was now growing successfully all over the world and was better protected.” It is listed as endangered on the IUCN Red List and would likely be extinct in its shrunken native range had awareness of its existence not come about when it did.

Fossil of Metasequoia occidentalis - photo credit: wikimedia commons

Fossil of Metasequoia occidentalis – photo credit: wikimedia commons

There are plenty of other interesting details to this story. Read the full article and check out the links on metasequoia.org to learn more. The account of Jiru Xue (also known as Hsueh Chi-Ju), the graduate student who collected the type specimens, is particularly interesting. Suprisingly, the tree Wang and Xue took their collections from is still alive today and is estimated to be over 400 years old.

Other longform article reviews on Awkward Botany:

Exploring Pollination Biology in Southwestern China

This is the sixth in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

Insect Pollination and Self-Incompatibility in Edible and/or Medicinal Crops in Southwestern China, a Global Hotspot of Diversity by Zong-Xin Ren, Hong Wang, Peter Bernhardt, and De-Zhu Li

We rely on pollinators to pollinate at least 75% of our food crops, which is why any talk of pollinator decline tends to make us nervous. It is also why research involving pollinators and pollination is so important. Despite all we know, there is still so much to learn. The authors of this study, recognizing that “there are large gaps in the study of the pollination of economically important and traditionally grown species in China,” set out to help close these gaps. Their research not only has the potential to benefit agricultural communities in China, but also adds to our growing understanding of pollination biology – a science that has become increasingly important in an age of human population growth and shifting climates.

The incredibly diverse Chinese flora includes at least 31,000 plant species. Three hundred of the 1500 species of worldwide cultivated crop plants “originated and/or were domesticated and/or underwent differentiation in China.” Southwestern China has a particularly large amount of botanical diversity and is considered a biodiversity hotspot. In this study concerning agricultural pollination, researchers chose to focus on Yunnan, a province in southwestern China. They chose this region due to its high level of current and historical agriculture and because it is “one of the last refuges of the eastern Asian honeybee, Apis cerana, in China.” They narrowed their research down to 11 species that are important for their culinary and/or medicinal use, some of them having widespread use and others having more local, cultural use. Depending on the species, conclusions were drawn either from available literature, from field studies, or both.

Eastern Asian Honeybee (Apis cerana) on Citrus limonia flowers (photo credit: www.eol.org)

Eastern Asian Honeybee (Apis cerana) on Citrus limonia flowers (photo credit: www.eol.org)

A review of the literature revealed information about each plant’s breeding system, the pollinators involved, ethnobotanical details, and other things. No information was available on the breeding system or pollinators of Panax notoginseng, “one of the most highly valued Chinese medicinal herbs.” Five species were found to be self-compatible (Angelica sinensis, Amomum tsao-ko, Brassica napus, B. campestris, and Gastrodia elata) and four were found to be self-incompatible (Camellia oleifera, Dendrobium catenatum, Fagopyrum esculentum, and Paris plyphylla var. yunnanensis). Codonopsis subglobosa was somewhere in the middle. The authors were intrigued by the persistent self-incompatibility in these domesticated plants (some more recently domesticated than others), noting that “both traditional and modern agricultural practices in China could not always overcome ancestral self-incompatibility mechanisms.” A running theme seemed to be that, if able to produce fruit or seed when hand-pollinated or without the aid of pollinators, the plants consistently performed better when insect pollinated. One of the most interesting findings was that Gastrodia elata, Dendrobium catenatum, and Paris plyphylla var. yunnanensis “persist in cultivation only through hand-pollination.”

Camellia oleifera, tea-oil plant, is pollinated by two native solitary bee species. It is avoided by native and introduced honeybees because its nectar contains substances that are toxic to worker bees, including caffeine, raffinose, stachyose, and galactose. Fagopyrum esculentum, common buchwheat, is native to southern China and was likely first domesticated there. It is pollinated by a variety of insects; however, its main pollinator in worldwide cultivation is the European honeybee, Apis mellifera. In China, evidence suggests that when pollinated by native pollinators, buckwheat produces higher yields and larger fruits. Codonopsis subglobosa is an undomesticated but cultivated perennial vine endemic to southwestern China, the roots of which are used as a substitute for ginseng. It can self-pollinate without a vector, but cross-pollination by wasps yields more seeds. Pollination by “hunting wasps” is rare, and C. subglobosa is not the only plant in the area pollinated by them. If the “evolution of hunting wasp pollination systems has evolved repeatedly in unrelated species native to southwestern China,” this region may be a “center for the convergent evolution of hunting wasp pollination.”

Common Buckwheat, Fagopyrum esculentum (photo credit: Wikimedia commons)

Common Buckwheat, Fagopyrum esculentum (photo credit: wikimedia commons)

Beekeeping has been a major part of agriculture in China for centuries. However, the introduction of the European honeybee has caused a significant decline in both wild and managed populations of native honeybees, despite native honeybees being “better adapted to more diffuse nectar resources” than the introduced honeybee. The decline in keeping and managing native honeybees is complicated and involves much more than just the introduction of the European honeybee. Along with the debate about what is best for agriculture in China, is the concern about what introducing non-native pollinators could mean for native flora and fauna. The authors conclude that there is “urgent need for new pollination management policies in China.”

This article ends with suggestions about how to improve and expand pollination biology research in China in order to fill gaps in knowledge, improve agricultural production, and protect and conserve native biodiversity. China is an ideal candidate for such research for several reasons: it has areas like southwestern China that are very species rich, it has a long history of agriculture, and it has numerous unique crops that are specific to Chinese culture. China also has a large and growing population, so improvements that can lead to more sustainable agricultural production will be greatly beneficial in the long run.