Ginkgo, Ducks Foot, ‘Ya Chio’, Silver Apricot ‘Yin Hsiang’, Maidenhair Tree
Image of a ginkgo tree in the Morton Arboretum. Sourced from a 2020 article written by Beth Botts in the Chicago Tribune. https://www.chicagotribune.com/lifestyles/home-and-garden/ct-home-garden-morton-0924-20200927-f5u47j5ravd6lmwqzrvtmfpspe-story.html
Botanical Identifiers (description)
The Ginkgo tree is easily identified by its unique fan-shaped leaves, and it is the sole remaining member of its evolutionary family, Ginkgoaceae (Isah 2015). This means all living ginkgo trees are very similar in appearance, there is wide variation in morphology between extinct species and the modern G. biloba. Based on fossils discovered belonging to extinct ginkgospecies, many structural differences are known to have existed in the leaves and reproductive structures (Figure 3) (Zhou, 2009). G. biloba leaves tend to have a single deep cleft in their middle, creating the bi-lobed appearance that the species is named for. In ancient species of ginkgo however, leaves may have had four or more deep clefts, causing some to appear compound or even needle-like in structure (Crane, 2019). Differences in reproductive structures between species were most pronounced in female individuals, showing many variations in the ovaries, including their placement, shape, and orientation in relation to other ovaries (Zhou, 2009). It’s unclear what has allowed ginkgo to survive its 250 million year evolutionary battle with so few changes, though its superior resistance to microbial, salt, and water stress likely played a role, and in the modern world it also makes ginkgo an excellent city tree (Kinoshita et al., 2021).
Fruit (A) and leaves (B) of Ginkgo biloba compared to sketches of the same structures belonging to now-extinct Ginkgo sp (C) (Crane, 2019).
Origin, Distribution, Habitat
G. biloba is part of an unusual classification of plants known as ‘living fossils’, named for their lack of phenotypic change throughout evolutionary time. The G. biloba tree we see planted on our roadsides today is nearly visually identical to the ginkgo trees that lived in the time of the dinosaurs, at least 200 million years ago (mya) (Zhao et al., 2019). Ginkgo first appeared amid the Triassic period, about 240 mya (Crane, 2019). From there, the ginkgo genus diversified throughout the Jurassic period and into the early Cretaceous period, continuing to flourish (Isah, 2015). It reached the peak of its diversity near the end of the Mesozoic era, however, approximately 100 mya, at the height of the Cretaceous period, ginkgo diversity began to decline, seemingly in conjunction with the rise of flowering plants and the drop in global temperature (Crane, 2019). Even with its reduced diversity, the family Ginkgoaceae survived the extinction event that killed the dinosaurs (known as the Cretaceous-Paleogene mass extinction), though its population became limited to the northern hemisphere (Crane, 2019). Over the course of the next 50 million years, the Ginkgoaceae population and its diversity would experience massive reductions during glacial periods, and recover to an extent during the warmer periods in between (Zhao et al., 2019). It was at this time that ancient Ginkgo spp. could even be found in the Canadian Arctic (Crane, 2019).
Modern G. biloba is descended from three genetically distinct ginkgo clades, each found in a different region of China (Zhao et al., 2019). The survival of these three distinct populations is due to their sequestering in three different geographically sheltered areas of China where other ‘living fossil’ plant species are also known to occur (Zhao et al., 2019). These areas are identified broadly as being in the south, east, and south-west of China, and they are considered refugia due to their sheltered nature. These refugia tend to occur in valleys or under the shelter of mountains, giving them a more temperate climate that is ideal for temperature-limited plants such as ginkgo (Zhao et al., 2019).
The reproductive strategy of ginkgo is quite unique, bearing the strongest similarities to the cycads, a palm tree-like group containing 305 living species (Delevoryas, 2016). Like cycads, ginkgo is a dioecious plant, meaning a tree will be either male or female, and pollination occurs by wind. The male trees have a cone-like structure that contains the pollen, and the females possess tiny and inconspicuous ovules at the ends of their branches, which produce a fruit, rather than a cone bearing exposed ovules in the fashion of a gymnosperm (Crane, 2019). Another similarity to the cycads, ginkgo possesses flagellated sperm, which are produced in the pollen grains. This is a relatively unusual trait in trees, and it tends to be a feature more reminiscent of ferns (Crane, 2019). These features all indicate that ginkgo was likely one of the earliest distinct trees to evolve (Delevoryas, 2016). In addition to this, it takes ginkgo an extremely long time to reach reproductive maturity, after approximately 35 years of vegetative growth (Isah, 2015).
History and Traditional Uses
Entry for Ginkgo nuts in the Bencao Gangmu (Chassagne et al., 2019).
The cultivation of ginkgo and its subsequent use in Chinese medicine and food has been practiced for centuries, spreading from China to Japan and Korea during the medieval ages (Crane, 2019). Approximately 1000 years ago is when ginkgo was first recorded to be actively cultivated by the Chinese for the harvest of its wood, leaves, and nuts (Crane, 2019). The earliest reference to the ginkgo tree in writing was from AD 980 in the text Ko Wu Tshu Than, (‘Simple Discourses on the Investigation of Things’), written by Lu Tsan-Ning (Crane et al., 2013).
The ginkgo seed itself is referred to as “bai guo”, and it was known historically that the ginkgo seed was poisonous to consume in its raw state, so it was often cooked when used in formulas (Dharmandanda & Fruehauf, 1998). The ginkgo seed was known to treat ailments surrounding the lungs, heart, bladder, and kidneys, as well as 8 skin disorders.
The ginkgo leaf was referred to as “bai guo ye” and although it is the seed that has the most prominently documented use in the Bencao, there are cases of regional usage for the leaves in various medicines and treatments (Dharmandanda & Fruehauf, 1998). The use of ginkgo leaves in medicine has been orally documented and written in regional folk medicinal documents for centuries, particularly in ginkgo-rich provinces (Dharmandanda & Fruehauf, 1998). It wasn’t until approximately 500 years ago, when the Imperial Academy of Medicine in China requested an official ginkgo leaf entry, that the ginkgo leaf was first introduced into the Bencao (Dharmandanda & Fruehauf, 1998). The Ming dynasty physician Liu Wentai wrote this new and updated version, called the Bencao Pinhui Jinyao (A Compilation of Essential Items of the Materia Medica) (Dharmandanda & Fruehauf, 1998). Ginkgo leaves were used to treat many of the same ailments that the ginkgo seeds were used for in addition to lung diseases and circulatory disorders (Dharmandanda & Fruehauf, 1998; Hatano et al., 2011; Chassagne et al. 2019).
Lastly, ginkgo roots, termed “bai guo gen”, were used rarely and were mostly found in folk remedies in ginkgo-rich regions (Dharmandanda & Fruehauf, 1998). Roots in particular did not have much use outside of treating the liver and kidneys because use of the seeds and leaves was more popular, as they were easier to acquire. Harvesting of ginkgo was done from September to October, as this was the season thought to promote optimal storage activity for all living organisms. (Dharmandanda & Fruehauf, 1998).
Cultivation methods of the ginkgo tree change depending on the type of product the trees will be used for. When the product being produced will be a food or ornamental, grafting is the technique most likely to be employed. Within the category of grafting, there are a couple of methods that can be used. The most common one is that the branches of an older tree will be grafted to the root stock of a seedling (Isah, 2015). This provides older branches with the means for the speedy initial growth that very young ginkgo trees have (Vaio et al., 2009). It also serves to massively reduce the time a tree must grow before it can produce seeds to as little as five years (Vaio et al., 2009). This method is quite valuable since the most common ginkgo food product is its nut (Isah, 2015).
In another method of grafting, male branches can be grafted to female plants. This is done for two main reasons. First, it is a practice sometimes carried out on trees associated with religious worship, as it represents the balancing of energies (Dharmandanda & Fruehauf, 1998). In the second case, it might be done for ornamental plants, because the female ovules produce an offensive smell, so female trees are less desirable for landscaping purposes (Isah, 2015).
Tissue culture is used as a method for production of ginkgo medicinal products, because this method of cultivation provides high chemical yields and ensures a uniform product (Isah, 2015). There are two very broad steps to go through in order to carry out this method. First is selection of parent plants that are high producers of the chemical of interest. In many cases, this might mean identifying a plant which just happens to naturally produce comparatively more of the molecule of interest, but for ginkgo, age of the parent plant is consistently important as well (Balz et al., 1999). Explants (the tissue samples used in production) have higher yield when taken from a parent plant between 5 and 10 years old, with yield lowering dramatically if older trees are used (Balz et al., 1999).
After selecting parent plants and producing explants, the next step is tissue culture. There are quite a few different methods for this, but none tend to be replicated easily. However, there are three methods that have seen some success. First is the culture of axillary buds to produce plantlets (Tommasi & Scaramuzzi, 2004). This method runs into one major issue, which is that the explants tend to produce a lot of callus and only occasionally include roots as well. In addition, the buds must be harvested from the parent plant at exactly the right time of year, or they will not be successful. It generally seems that the very end of winter is the best time to do this (Tommasi & Scaramuzzi, 2004). The next method is the culturing of specific tissues that possess the highest concentration of the target molecule. In ginkgo, many of the medicinal compounds are produced in the roots and carried up to the rest of the plant, but unfortunately, ginkgo root tissue does not tend to grow well in vitro (Balz et al., 1999). The last method is to isolate a ginkgo embryo and inoculate it into the culture medium (Isah, 2015). This method tends to have more success, and even though the other two methods could theoretically be more productive, this method at least allows for many seedlings to be started in an extremely small area, which will be good for protecting and maintaining the ginkgo population as ginkgo products increase in demand.
Ethnobotanical Uses / Cultural and Spiritual Significance
In Japan, China, and Korea Ginkgo is highly important for its symbolism in Buddhism, Daoism, Confucianism, and Shintoism, as well as general arts and culture (Crane, 2019). The ginkgo tree was considered a physical manifestation of the Daoist concept of yin and yang as well as a symbol of elegance, longevity, and vitality (Dharmandanda & Fruehauf, 1998). In many Daoist temple courtyards, there are ancient ginkgos that are thousands of years old, some of which appear to predate the temple structures. The age of these trees indicates the possibility of earlier shamanic worship that may have led to the building of a temple in honour of the tree (Dharmandanda & Fruehauf, 1998).
In Daoism, the ginkgo symbolizes sacred life force and is the living witness of the sages and holy folk that are said to have laid the foundations for Chinese civilization today.
Many ginkgo trees are also found in Buddhist temples and Shinto shrines in Japan, Korea, and China (Crane, 2019). Ginkgo wood is used to carve sacred statues and many ginkgos at these places of worship are adorned with inscriptions and ribbons that express hopes and prayers to the gods of the locals (Crane, 2019). Ginkgo was also very symbolic to Confucius, who was known to prefer sitting under ginkgo trees or on platforms of their wood when delivering his teachings (Crane, 2019).
Ginkgo illustration in the Kinmo Zui, a Japanese encyclopedia-like pictorial dictionary published in 1666. (Crane et al., 2013).
In China, the Imperial family played a very important role in popularising the cultivation of ginkgo, and they are responsible for the subsequent flood of ginkgo into Chinese art and poetry in the 11th century (Crane et al., 2013). The ginkgo tree was brought to the Chinese capital by the emperor’s son-in-law, and its image began to permeate the art scene of the 11th and 12th century (Crane et al., 2013). In Japan, the ginkgo leaf has also been incorporated into many facets of art and culture. For instance, it has been incorporated into the family crests, also known as a mon, of many different ancient families (Crane et al., 2013). As well, the ginkgo leaf first began appearing on traditional Japanese kimonos in the 15th century with maple, oak and pine leaves (Hori & Hori, 1997). This pattern is called a fukiyose, which is popular to this day on scarves, ties, autumn kimonos, and obis (Hori & Hori, 1997). The topknot was also a popular hairstyle for Japanese men during the Edo period (1600’s-1800’s) and often this hairstyle was referred to as ‘ginkgo’ because the tip was ginkgo leaf-shaped (Hori & Hori, 1997).
Specific combinations and doses of 14 compounds identified in the stem bark were able to increase or decrease the activity of specific proteins and receptors (Ngan et al., 2012). Thus, the bark has the ability to prevent and treat health related issues including metabolic and inflammatory diseases, cancer and AIDS. As well, more in depth research is being conducted on its use in reducing insulin resistance and normalizing glucose levels in diabetics (Ngan et al., 2012).
The fruit of G. biloba are rich in riboflavin, vitamin C, carbohydrates, proteins and other essential nutrients and for these reasons are another well-known ingredient in both the culinary and medicinal world. Extract from the seeds are able to significantly decrease the infiltration of inflammatory cells, such as lymphocytes in an asthmatic airway, thus relieving any airway inflammation (Tang et al., 2007). The proteins within the seeds and seed coats have been found to contain compounds such as flavonoids and terpenoids, which allow it to exhibit strong antioxidant, antimicrobial and insecticidal properties (Wang & Zhang, 2019). For those suffering from skin infections such as acne, psoriasis, dermatitis and eczema, the seeds are able to inhibit the growth of biofilm formation of common skin pathogens involved in these infections (Chassagne et al., 2019).
The predominantly used part of the ginkgo tree are its leaves, as it contains higher concentrations of the compounds needed for disease treatment. However, within the leaf, it is the extract that is most used in modern medicine. This extract, termed EGb761 contains 24% flavonoid glycosides, 6% terpene lactones and less than 5 ppm ginkgolic acid (Mahadevan & Park, 2008). However, it is ginkgo’s antioxidant properties that are the main aspect which affects chronic ailments including neurodegenerative diseases, cardiovascular diseases and cancer. The main focus being the prevention of neurodegenerative diseases, such as Alzheimers and memory loss (Mahadevan & Park, 2008). It has been discovered that Alzheimer’s disease is linked to the amyloid beta peptide, Aβ, which is the same peptide that is inhibited by ginkgo leaf extract (Mahadevan & Park, 2008). In addition, ginkgolide B and bilobalide from the ginkgo leaf extract is able to decrease the occurrence of apoptosis, which is the leading cause for neurodegenerative diseases. These bioactive compounds also increase the cerebral blood flow via stimulation of norepinephrine secretion (Mahadevan & Park, 2008).
Diagram displaying the various secondary metabolites in G. biloba and their effects and benefits (Liou, 2010).
Market Status / Economic Value
As G. biloba is an incredibly useful plant, it is not surprising that it dominates amongst other medicinal plant species. In a seven billion dollar industry the use of ginkgo continues to accelerate rapidly, ranking first among herbal medicines, and research is continuously confirming uses employed by TCM (Ngan et al., 2012). In 2008, there were approximately 142 ginkgo products on the global market and the utilization of this tree is still increasing, especially for treating blood and memory disorders (Ngan et al., 2012).
The difficulty in keeping up with demand for ginkgo products comes from two key factors: ginkgo is extremely slow growing, it takes an average of about 35 years before the tree will reach maturity (Isah, 2015). In addition to this, when seeds are produced, a large portion of them are not viable. For this reason, growing ginkgo from seed or for its seeds can be an extremely slow process. Ginkgo appears to be one of the species which benefits from climate change, with increased range and better health (Guo et al., 2021). However, climate change will also lead to a decrease in the concentration of medicinal molecules in the plant. Should this happen, more ginkgo will have to be harvested to meet the same demand (Guo et al., 2021). While climate change may not directly impact the survival of ginkgo, it could still lead to overharvesting and further endanger its population.
As ginkgo is known to beneficially prevent neurodegenerative diseases, many studies have aimed to understand if extract EGb761 is able to prevent dementia (Mahadevan & Park, 2008). Several of these studies have shown positive outcomes on dementia patients taking the ginkgo leaf extract, however many other studies have disproved these results. Thus, it would be advantageous to perform further testing to confirm the results of either side. In addition, much is still left to learn about G. biloba’s anticancer properties. A few studies have displayed the effects of its bioactive compounds on tumor suppression, yet further research is required to be able to confidently use EGb761 on patients (Mahadevan & Park, 2008).
About the Authors
From left to right: Sarah, Vanessa, Sofia.
Sarah is a fourth-year student who is completing a bachelor’s degree in plant science at the University of Guelph. She currently is focusing her studies on plant pathology, as well as the impacts that plants and plant diseases have had on human history and culture. Sarah is currently working on an undergraduate student research project that is focusing on using RNAi as a biopesticide to combat Spotted Wing Drosophila. Sarah hopes to be able to further her education next year by pursuing a master’s degree.
Vanessa is a fourth-year student at the University of Guelph pursuing a BSc in Plant Science, emphasizing in Botany. She will be graduating in 2022 and then hopes to pursue a master’s degree in plant tissue culture at GRIPP. She is passionate about medicinal and endangered plant species and aims to further research efforts in these areas.
Sofia is a fourth-year student studying Plant Science at the University of Guelph. Her interests within the field include the possible uses of plant secondary metabolites in medicine and agriculture, and the mechanisms through which plants can adapt to harsh or ever-changing environments. Sofia is currently researching the applications of CRISPR systems in creating plant crops that are more resilient in the face of climate change.