Ginkgos and People2014 A Thousand Years of -~ II

Interaction

Peter Del Ttedici

Recent discoveries on the effects of Ginkgo leaf extract in promoting bloodflow have stimulated renewed interest in this ancient plant.

Above all else Ginkgo biloba is a survivor, notonly of the ravages of geological time, extend-ing back at least 70 million years to the Paleo-cene, but also of the ravages of human time,the so-called Internecine. Indeed, the Ginkgotree has a documented history of cultivationby the Chinese for close to a thousand yearsand an undocumented history that no doubtextends back much further.As a result of this interaction, Ginkgo

biloba has become so closely intertwinedwith human beings that its existence outsideof cultivation has been the focus of anunresolved debate for over a hundred years. Inthe Western literature, Buddhist monks arewidely credited with preserving Ginkgo fromextinction by planting it in their templegardens (Wilson, 1920), but little documentedevidence supports this notion. The argumentof H. L. Li (1956) that the tree was first culti-vated for its edible and medicinally activeseeds provides a more plausible, if somewhatless romantic, motivation for its preservation.As a wild species in China, Ginkgo was

probably a member of the temperate, mixedmesophytic forest that once covered the hillcountry bordering the Yangtze River valley formost of its three-thousand-kilometer length.

Most of this forest has now been cut downexcept for remnants found in a few isolated

valleys and on a few steep mountainsides(Wang, 1961). During the fall of 1989, theauthor and his colleagues, Professor HsiehLing of the Zhejiang Forestry Department andGuang Yang of the Nanjing Botanical Garden,visited one such area in eastern China, thefamous Tian Mu Mountain in ZhejiangProvince, where Ginkgo biloba still grows ina semi-wild state. Our ecological observationsmade on Tian Mu Shan indicate that Ginkgois well adapted to growing on disturbed siteswhere light intensity is high, particularlyalong stream banks, on rocky slopes, and onthe edges of exposed cliffs (Del Tredici et al.,in press).The purpose of this article, however, is not

to examine the question of whether Ginkgostill exists in the wild but to examine themutually beneficial interactions that haveoccurred between Ginkgo biloba and Homosapiens over the last one thousand years. Fromthe botanical perspective, these interactionshave resulted in a tremendous expansion ofthe tree’s range from its native Chinese homeinto every country in the temperate world.From the human perspective, the interactions

Figure 1. One of the largest Ginkgos in Asia, growing on the grounds of Yongmun-san temple in Korea. The tree,about 60 meters tall and 5 meters in diameter, is reputed to be 1100 years old. Photograph by S. A. Spongberg.

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The Quintessential Survivor

Ginkgo is considered to be one of the tough-est of all cultivated trees, a belief borne out

by a famous specimen growing near thehypocenter of the 1945 atom bomb blast overHiroshima, Japan. According to Michel andHosford, the tree that still grows there todaysurvived the bomb by sprouting from its baseafter its trunk was completely destroyed!Another indication of Ginkgo’s exceptional

power of survival is its long life span.Throughout Asia there are many large andancient specimens that are in excess of a thou-sand years old (Figure 1). (Miyoshi, 1936; Ling,1965; Spongberg, 1978). According to Profes-sor Ling of the Zhejiang Forestry Department,the largest and perhaps oldest Ginkgo inChina is a specimen growing in Folaishan inJu County, Shandong Province. It is an ovu-late (female) tree, approximately three thou-sand years old, with a diameter at breastheight (DBH) greater than 4 meters and aheight of 26.5 meters. In Zhuji County,Zhejiang Province, the author saw one oldovulate tree with a DBH of 2.3 meters and aheight of 33 meters (Figure 2). In 1988 this treeproduced a remarkable 379 kilograms ofcleaned nuts. If Ginkgo is indeed a pioneerspecies, as our work on Tian Mu Shan sug-gests, then it must be considered a persistentpioneer that can outlast several successionalcycles.Under cultivation, Ginkgo is considered

highly adaptable, growing well in most partsof the temperate world with a distinct season-ality and moderate rainfall, including areaswith a Mediterranean type of climate as wellas those with a cold temperate climate, wherethe minimum winter temperatures can reach-30 degrees C. Ginkgo seems to grow bestwhen planted in full sun, although it alsoshows the ability to persist indefinitely underconditions of low light, such as when plantedalong the cavernous, downtown streets ofmany cities in eastern North America.

Figure 2. An ancient ovulate Ginkgo growing in YangTang village, Zhejiang province. The tree had adiameter of 231 centimeters and was 33 meters tallin 1989. In 1988 the tree produced 379 kilograms ofcleaned nuts.

According to reports in the horticulturalliterature, Ginkgo will grow in a wide varietyof soil types (with the exceptions of those thatare very wet or alkaline or show a pronouncedhardpan) but it prefers soils with a pH of 5.5to 6.5. Under typical conditions of outdoorcultivation, the roots of most Ginkgos areinfected by vesicular-arbuscular mycorrhizae(VAM) that play an important role in theuptake of the element phosphorus (Bonfante-Fasolo and Fontana, 1985; Fontana, 1985).

In addition to its great powers of survival,another characteristic that makes Ginkgo aparticularly successful street tree is its highdegree of resistance to insect damage and tofungal, viral, and bacterial diseases, relativeto other cultivated trees. Contrary to the

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numerous anecdotal reports, however,Ginkgo’s tolerance of air pollution, particu-larly sulfur dioxide and ozone, is not thatmuch better than other trees, and the tree isno less susceptible to damage from ionizingradiation than other gymnosperms (Major,1967; Hepting, 1971; Sharma, 1989).Under conditions of moderate soil fertility,

Ginkgo grows quite rapidly, averaging up tohalf a meter per year when young. With theonset of sexual maturity, between 20 and 30years, height growth generally slows down asthe tree fills in its rather sparsely branchedjuvenile framework. At full maturity, Ginkgois not a particularly tall tree, reaching a max-imum height of about 30 meters, althoughone specimen in Korea has been measured at60 meters (Figure 1) (Spongberg, 1978).

In the fall of 1989, I interviewed horticul-turists in Shanghai, China, who worked for adivision of the Ancient Trees ManagementGroup of the Shanghai Public GardenAdministration. They had catalogued andmeasured the height and girth of all the largeGinkgos in the province, and had found a totalof four hundred trees over one hundred yearsold, half of which were over three hundredyears old. They were willing to share theirfindings concerning the growth of Ginkgoonly in qualitative terms, and told me that thegrowth rate in Ginkgo, measured in terms ofcentimeters of girth increase per year, is rapidand increasing between the ages of 1 and 40years. Growth rate slows down between the

ages of 40 and 110 years, and between the agesof 110 and 150 to 200 years, it is more or lessconstant. From 150 to 200 years and beyond,the growth rate of Ginkgo appears to

diminish.

Cultivation in the West

Ginkgo was introduced into Europe fromJapan at the Botanic Garden in Utrecht, Hol-land, about 1730, where a tree that is proba-bly one of the original introductions is stillin very good condition (Dallimore and Jack-son, 1966). In Kew Gardens, England, a

Ginkgo is still growing that was planted in1754 and was probably part of the original

introduction into that country. The first

Ginkgo reported to produce fertile seed inEurope was a large male tree growing in theBotanic Garden of Montpellier, France, in1835. This anomalous situation was broughtabout by the fact that scions from a femaletree (growing near Geneva, Switzerland) hadbeen grafted onto it some years earlier. This"hybrid" tree was still alive and in good healthwhen the author visited the garden in 1990.The first report of a Ginkgo growing in

North America comes from a letter by Wil-liam Hamilton of Philadelphia to his privatesecretary, Mr. Smith, who was in charge of hisestate, Woodlands, in his absence. Writingfrom London on November 2, 1785, Hamiltonadmonishes Smith:

The Cistus’s the Heaths, eleagnus, Ginkgo, Laurus’s,Tamarisks, Yucca glonoso, the Carolina mahogany,Zantoxylon sempervirens &c, should be secured byskreens of Dry straw or some other means, but by[no] means let dung be put to their Roots for it willinevitably kill them ... (Smith, 1905)

While one staminate individual from this

original introduction of Ginkgo was still aliveand well in 1981, growing on the grounds ofwhat is now the Woodlands Cemetery inPhiladelphia (Del Tredici, 1981), the tree hassince been cut down. Although there are norecords to prove it, a large Ginkgo growingnearby in William Bartram’s garden is thoughtto be a siblmg of Hamilton’s tree (Harshberger,1920) and is now assumed to be the oldestGinkgo in North America (Figure 3).

In the early 1800s, Ginkgo began to begrown in many parts of the United States,primarily in the private gardens of wealthyindividuals. Remarkably, many of these earlyintroductions are still alive and healthy. In1841, the nurseryman and horticulturistAndrew Jackson Downing was among the firstAmericans to advocate the use of the Ginkgoas an ornamental:

As the foliage is of that kind which must be viewednearby, to understand its peculiarity, and as the formand outlme of the tree are pleasmg, and harmonizeswell with buildings, we would recommend that itbe planted near the house, where its unique charac-ter can be readily seen and appreciated.

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Figure 3. The Bartram Ginkgo, presumably the oldestspecimen in North America, planted circa 1784.When photographed in 1988, its height was 32 metersand its diameter at breast height was 103centimeters.

According to C. S. Sargent, the first Ginkgoto produce fertile seed in North America wasa specimen growing on the grounds of theformer Kentucky Military Institute in Frank-furt, Kentucky, in 1877. These trees wereplanted in the 1850s by Henry Clay, who, asan influential United States senator, hadsomehow acquired them directly from Japan(Del Tredici, 1981). Within the next ten years,many of the trees growing in Washington,D.C., were producing large quantities of seed,which were widely distributed to nurseries onthe east coast (Falconer, 1890).With the exception of a few saplings that

came directly from Japan, it appears that most

of the oldest Ginkgos growing in NorthAmarirn «>nrc from 1:.......cr1......,....r1 ---- on~. &.¿.&..&._......-... tt"",.a.,-, ..&..&..&..&..1"’’’’’’’’’’’’’’’’’’’’’’’ .......-...........A..J.A."’-b.&.-""",,,,,,,,,,,,u u_---

lings, which most likely had been raised fromimported Japanese seed. By the late 1800s andearly 1900s, after the original Americanintroductions started producing seed in abun-dance, Ginkgo became popular as a street treeon the east coast, primarily in urban areasfrom Boston to Washington, D.C. (Corbett,1903). Its tolerance of the particulate air pol-lution produced by burning coal was highlytouted by horticulturists of the day, along withits high degree of resistance to fungal diseasesand insect pests.The horticulturist’s love affair with the

Ginkgo began to fade in the 1920s and 1930swhen many of the widely planted seedlingstreet trees began reaching sexual maturity.At this point, ovulate trees started producinglarge quantities of seeds, which, whencrushed by passing foot traffic, resulted in afoul-smelling mess, reminiscent of the odorof vomit. In the horticultural literature, thisscent is variously referred to as "disagreeable,""evil "offensive," "disgusting," "repulsive,’"nauseating:’ and "abominable." To make mat-ters worse, the odoriferous sarcotesta containsanacardic acid, a compound known to causea severe skin rash on those who happen totouch or walk barefoot on the seeds (Mitch-ell and Rook, 1979).

Vegetative PropagationIn response to the perceived litter problemposed by the production of seeds by femaleGinkgo, Western horticulturists generallyrecommend the planting of vegetativelypropagated male plants for street-tree use.Over the years, many male clones have beenselected for this purpose, along with clonesdisplaying a wide variety of distinctive leafand habit characteristics (Santamour et al.,1983).Most Ginkgo clones are remarkably easy to

propagate vegetatively either from cuttings orby grafting. The author has had good successrooting cuttings of Ginkgo at virtually anytime of the year, including: (1) softwood cut-

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Figure 4. 7bpophytic effects in Ginkgo biloba. This rooted cutting was originally collected from a mature treein February 1989. The photograph, taken in May 1991, clearly shows the "fixed" horizontal orientation of newgrowth.

tings collected in summer and placed underintermittent mist; (2) hardwood cuttingstaken in the fall at the time of leaf drop; and(3) hardwood cuttings taken in the spring justprior to bud break. While treatment withindolebutyric acid (IBA) does not seem to benecessary in order to achieve a high percen-tage of rooting (Doran, 1954), there does seemto be some variation in the rooting responseof different individuals, perhaps due to the ageor vigor of the tree they were taken from (Ver-meulen, 1960). Despite their high degree ofrootability, Ginkgo cuttings usually growslowly the first season following propagation,producing only rosettes of leaves and littleextension growth. It is not until their secondgrowing season that they will produce longshoots. For this reason most nurseries preferto propagate Ginkgo by grafting scions ofselected cultivars onto seedling rootstocks, aprocedure that results in abundant extensiongrowth during the first season of growth.

Although the preferential planting of maleclones is widely recommended in the hor-ticultural literature, one very important facthas made this goal largely unattainable: thevegetative propagations of Ginkgo, whetherfrom cuttings or grafts, generally suffer froma developmental problem known as topophy-sis. Topophysis is defined as the organizationalstatus of a meristem that is determined by itsposition on the plant and that remains stablethrough vegetative propagation (Halle et al.,1978). In other words, if a lateral branch ofGinkgo is rooted or grafted onto a seedlingrootstock, the resulting propagule will con-tinue growing in the direction it maintainedwhile it was still attached to its parent trunk

(Figures 4 and 5). This means that vegetativelypropagated Ginkgos seldom show thedominant central leader and whorled brancharrangement typical of seedlings. Instead, thebranches grow out at erratic angles, produc-ing low-branched trees with poor form from

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Figure 5. Rooted cuttings from a single branch ofGinkgo biloba ’Fastigiata’AA #144-39-A. Softwoodcuttings were taken in August, 1981 and rooted underintermittent mist. (top) The two cuttings on the leftwere taken from diagonally growing lateral shoots,while the one on the right was taken from the verti-cal termmal shoot. Photographed in December 1985.(bottom) The same cuttings photographed in Febru-ary 1991. For scale, the index card is 7 centimetersby 13 centimeters.

the point of view of street-tree plantings.The only way that nurseries have been able

to circumvent the problem of topophysis isthrough the practice of "stooling" in whichyoung stock plants are repeatedly cut backlow to the ground to stimulate the productionof numerous vertical replacement shoots.When these vigorous terminals are used aspropagation material, they will produce a ver-tically growing tree. According to WilliamFlemer of Princeton Nurseries, this techniqueseems to work particularly well with fastigi-ate (upright) clones of Ginkgo in which manyof the laterals tend to possess a vertical orien-

tation to begin with. At the present time suchfastigiate trees are the only male Ginkgoselections that are widely available to thegeneral public.

Cultivation for Nut Production

While Western horticulturists have concen-trated on the ornamental uses of Ginkgo,Asian horticulturists have focused their atten-tion primarily on the cultivation of the treefor its edible nuts. According to Dr. Frank San-tamour and his colleagues (1983), Chinesehorticulturists have selected at least 28 vari-eties based solely on the size and shape of theedible nut. Ginkgo nuts are highly nutritiousand, when fresh, consist of 37.8 percent car-bohydrate, 4.3 percent protein, and 1.7 percentfat (McCarthy and Matthews, 1984). Whilemost of the carbohydrate is in the form ofstarch, small amounts of sucrose, glucose, andfructose are also present, giving the nuts asweet taste.

When Ginkgo is cultivated for its ediblenuts, the cultivar is generally grafted onto aseedling rootstock. As is the case with vegeta-tively propagated cultivars in North America,the grafted Chinese trees show strongtopophytic effects (Figure 6). When the authorwas in eastern China during the fall of 1989,he visited Dongting Mountain on the shoresof Lake Tai in Jinagsu Province. This well-known Ginkgo nut-producing area is thehome of the famous cultivar ’King of Dong-ting Mountain,’ which produces the largestnut of all Ginkgo cultivars (Figure 7). Oldgrafted trees in Dongting Shan were scarcelymore than five meters tall and were branchedlow to the ground. They tended to lack botha central leader and whorled branches. Whilesuch a shape would be undesirable in a treecultivated for ornamental purposes, it is con-sidered advantageous in terms of nut produc-tion because it facilitates harvesting. Thissituation provides a clear example of the"domestication" of a plant by selective propa-gation.

In conversations with agriculturists whocultivated Ginkgo for its nuts in Zhuji Xianin Zhejiang Province, the author learned the

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Figure 6. A grove of grafted Ginkgos cultivated for them edible nuts on Dongtmg Shan, Jiangsu Province, China.

following about the commercial productionof Ginkgo nuts:

1. Ginkgo bears a heavy crop of seeds everyother year, with relatively light crops in alter-nate years.

2. The grafted female trees produce nutsthree to five years after grafting, as opposedto the twenty to thirty years it takes for seed-lings to begin bearing.

3. In the older Ginkgo nut plantations, themale/female ratio was about 1 per 100. Thisratio has been raised to 3 to 5 per 100 in recenttimes, leading to more effective pollinationand greater nut production.

4. For successful pollination of female trees,the distance of the nearest male tree to thefemales is not as critical as (a) the size of themale tree-the taller it is, the better the pol-lination ; (b) the direction of the wind-maletrees should be planted upwind of females toachieve maximum seed set; and (c) the

presence of barriers, such as buildings, whichcan inhibit the flow of pollen.

5. Seed production can be increased bymanually placing branches of male trees

within the crown of female trees during thetime of pollination (Ling, 1983).

In China, the processing of the nuts for mar-ket is a very straightforward process. Eitherthey are knocked off the trees in mid-

September with long bamboo poles, or theyare collected from the ground shortly afterthey fall. After collecting, they are allowed tosit for a few days in plastic containers, untilthe fleshy outer coat begins to soften (andsmell). At this point the seeds are washed inrunning water so that the fleshy outer coatrises to the top and can be poured off, leavingthe heavy nuts to sink to the bottom. It isimperative to wear gloves during this processsince the fleshy coat contains anacardic acid,which causes a severe rash in many people.

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Figure 7. The exceptionally large nuts produced bythe Ginkgo cultivar ’King of Dongtmg Mountain’ onthe top, with a more or less typical Ginkgo nut onthe bottom. Scale is m millimeters.

After the seeds are washed, they are spread outto air-dry for one to two weeks, at which pointthey are bundled up and put in a cool environ-ment for storage.Raw Ginkgo nuts, which are rich in lipid

compounds, are considered toxic to humans,and it is in this state that they are used in

traditional Chinese medicine (Perry, 1980). Formirnncpc nr MOTTm^rl-ir* Bry a I rnncumntinn *-li£»f """ ’"" f *-"~’’** W *"**~ ~~~~~~~"~~2022~~~~~~~~~»2022~~»* *2022-.~2014 *.*.****. W......U ».*^.>.£S W... V.*..*.^ V"V

seed must be cooked. Usually they are boiledin water until the hard shell cracks open andthe kernel can be removed. Traditionallyeither these kernels are boiled in sugar waterto make a sweet soup or they are pan-fried andeaten plain. They can also be mixed in withother ingredients. The flavor and texture ofthe Ginkgo nut are reminiscent of the sweetchestnut, Castanea sativa. In several placesI visited in China, I was warned not to eatmore than seven Ginkgo nuts at one sitting;otherwise I would experience toxic sideeffects. Young children, in particular, are

warned about eating too many Ginkgo nuts.Because Ginkgo nuts are considered a

delicacy throughout Asia, they sell for a con-siderable amount of money per kilogram.Most of the seeds that are produced in Chinaare sold to foreign buyers, who, in 1988, paid5 yuan per kilo (approximately $1.50). Theprice was depressed to 3 yuan per kilo in 1989as a result of a lack of foreign buyers causedby the Tiananmen Square disturbances in thespring of that year.Chinese living in other Asian countries are

the principal consumers of the crop, althougha substantial amount of seed is also shippedto Chinese population centers in Europe andNorth America. While the author was unableto obtain exact figures on total seed produc-tion for China, he was told that in 1984 theyield was more than 5 million kilograms ofdried seeds.

Ginkgo as MedicineThe Ginkgo tree is apparently mentioned inthe oldest Chinese herbal, Shen Nong BenCao ling, dating from 2800 B.C. (Michel andHosford, 1988). Specific reference to themedicinal use of the leaves, however, does notcome until 1436 (in Lan Mao’s Dian Nan BenCao), which recommends the external use ofthe leaves for treating skin and head sores, aswell as freckles. The first mention of the inter-nal use of Ginkgo leaves comes in 1505 in atext by Liu WenTai, Ben Cao Pin Hue fingYaor. In modern Chinese medicine Ginkgo

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leaf preparations are recommended as

"benefiting the brain," as an astringent to thelungs, and to relieve symptoms of asthma andcough (Foster, in press).Numerous pharmacologically active consti-

tuents have been extracted from the leaves ofGinkgo, such as flavones, biflavones, organicacids, and flavonoid glycosides, includingkaempferol, quercetin, and isorhamnetine. Itis the diterpene lactones, however, includingginkgolides A, B, C, J, and M, and thesesquiterpene, biloablide, that have arousedthe most interest and have been the focus ofmost modern research. A, B, and C are foundboth in the leaves and the "bark" (cortex) ofthe root, while J is found only in the leavesand M only in the root cortex (Boralle et al.,1988).The ginkgolide compounds are unique

20-carbon cage molecules that possess anelectron-rich cavity ideally suited for the bind-ing of cations or polarized molecules (Figure8). Recently, Professor E. J. Corey and his col-leagues at Harvard University have synthe-sized ginkgolide B under laboratoryconditions, but the prohibitive cost of theprocedure makes it unlikely that a syntheticproduct will ever replace the natural extract.The ginkgolides also show varying degrees

of potency as specific antagonists of platelet-activating factor (PAF), a compound identifiedas a crucial mediator of a wide range of phys-iological processes and pathological condi-tions. Of the five naturally occurringginkgolides, B is considered the most activefrom the point of view of antagonizing PAF(Braquet, 1988, 1989).Numerous pharmacological and clinical

studies with Ginkgo leaf extract have demon-strated a positive effect in increasing vaso-dilation and peripheral blood-flow rate in thecapillaries of patients suffering from a varietyof circulatory dysfunctions. In Europe, theGinkgo leaf extract is most popular among theelderly, who take it either to treat the minorsymptoms of aging, such as dizziness, ringingin the ears, and short-term memory loss, orto treat the side effects of major disorders,such as Alzheimer’s disease. In one series of

Figure 8. The chemical composition of ginkgohde B,a unique 20-carbon cage molecule with a tert-butylegroup (tBu) and methionine (Me) Incorporated intothe framework. The electron-nch cavity, formed bythe three lactomc groups (-OC= O), is ideally suitedfor the binding of positively charged cations.

tests, Ginkgo extract has been shown toincrease short-term memory function in bothhealthy, young volunteers and elderly patientssuffering from vascular disorders (Hindmarch,1988).

Positive results with the extract have alsobeen achieved in the treatment of the inflam-mation of the bronchial airways associatedwith asthmatic attacks. The extract was moreeffective in the treatment of asthma whenadministered directly into the lungs as an aer-osol rather than taken orally (Roberts andBarnes, 1988).Ginkgo leaf extract has also been proven

effective in the treatment of arthritis, airwayhyperactivity, thrombosis, endotoximea, poorblood circulation, and gastrointestinal ulcer-ation. It has also been shown to be useful inthe treatment of various eye, ear, and skin dis-eases. After nearly fifteen years of clinicaltrials in Europe, there are no reports of toxicside effects.

Ginkgolide CultivationGinkgo has been cultivated specifically for thepurposes of leaf production for ginkgolideextraction since 1982, when large-scale plant-ings were established in Bordeaux, France, and

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Figure 9. The Ginkgo plantation in Sumter, South Carolina, in early spring. For scale, the individual segmentsof the irrigation system are about 45 meters long.

in Sumter, South Carolina. Seedlings are

planted 40 centimeters apart in rows onemeter apart, comprising a stand of approxi-mately 25,000 trees per hectare. For the 400hectare (1000 acres) plantation in Sumter, thisamounts to an amazing 10 million Ginkgos-surely the largest Ginkgo forest on earth, atleast since the Paleocene (Figure 9).

In Sumter, the leaves are harvested frommid-August to mid-September while they arestill bright green, and the resulting yields arebetween 3,000 to 4,000 kilograms of driedleaves per hectare (2,640 to 3,520 pounds peracre). The trees are severely pruned in thewinter following the harvest to induce mul-tiple branching and to keep the plant smallenough to make it possible to harvest theleaves mechanically (Figure 10) (McClintic,1991).

Freshly havested Ginkgo leaves have a

moisture content of about 75 percent.Moisture is reduced to 12 percent by passagethrough a gas-fired, 15-meter-long rotary drumdrier. The dried leaves are then compactedinto 180-kilogram bales, wrapped in burlapand polyethylene, and then loaded into con-tainers and trucked to Charleston, SouthCarolina, where they are loaded on a ship thattakes them to extraction plants in Europe.

In Europe, the extract is marketed under thebrand names "Thebonin,®" "Tanakan,©" and"Rokan,®" and gross annual sales in 1988amounted to about $500 million (Corey et al.,1988). While the use of Ginkgo leaf extractshas proved to be very popular both in Asia andin western Europe as a prescription drug, theproduct has yet to be marketed to any greatextent in the United States. This unavailabil-

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Figure 10. Some of the highly variable, and exceptionallylarge, leaves produced by the heavily fertilized Ginkgosgrowing on the plantation in Sumter, South Carolina. Scale bar at the lower left is 10 centimeters long. Someleaves are so highly dissected that they might almost be considered compound.

ity is primarily due to the fact that the extractdoes not meet the purity standards of theUnited States Food and Drug Administrationfor prescription drugs. As a result, the extractis only available in health food stores as arather expensive herbal remedy. It is soldunder a wide variety of names, but mainlythese products are just a repackaging of theproducts produced in Europe. At this point,it is unclear if Ginkgo leaf extract will everreceive FDA approval as a prescription drugavailable to consumers in the United States.

AcknowledgmentsThe author would particularly like to thank Dr P. Bra-

quet of the Institut Henri Beaufour, Dr J.-P. Balz of Gar-nay Inc., Dr. R Cook, Director of the Arnold Arboretum,Dr S.-A. He, Director of the Nanjing Botanical Garden,and Dr. R. B. Primack of Boston University for their sup-port and encouragement with this project. S.-L. Miao

assisted the author with Chinese translations. Much ofthe work presented here is part of the author’s Ph.D dis-sertation at Boston University on Ginkgo biloba, com-pleted in the spring of 1991.

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Peter Del Tredici is editor of Arnoldia.