Maidenhair Tree (Ginkgo biloba)

Issue: 
March-April 2010

THE MAIDENHAIR TREE, GINKGO BILOBA, is easily the most unique tree on earth. Like the coelacanth, it is a living example of a species group that was thought to be extinct and known primarily from fossil records. Ginkgophyta fossils appear prior to, and concurrently with, the dinosaurs. Ginkgos have basically been around for about 150 million years. Numerous extinct species of Ginkgo have been identified from fossilized remnants, but G. biloba is the only extant species. As spermatophytes, ginkgos are one of only two plant types that have free-swimming sperm and are considered by botanists to be the evolutionary link between spore producers (e.g., ferns, mosses) and gymnosperms.

It is generally accepted that the maidenhair tree is native to only one coastal region of China, though it has a long history of cultivation, usage and reverence in several oriental cultures. The species has only been known to western botanical science and horticulture since the late 1600s. Over the last 300 years, the propagation and cultivation of ginkgo has expanded considerably, and many varieties of this tree now grow in North America, Europe and elsewhere.

Status
This species has been introduced to North America, including many communities across Ontario. Non-native species, including naturalized ones, are not listed in any provincial or federal species-at-risk legislation, but they may still have some local protection in jurisdictions with effective tree preservation bylaws. The ginkgo’s global risk status is currently listed as endangered by the IUCN.

Description

Leaves. Leaves are simple, uniquely fan-shaped and parallel-veined. Their average length is 5-10 cm and they tend to grow in clusters from dwarf shoots at the terminals, as well as inner canopy portions, of twigs and branches. They lack a midrib and there is usually a single apical sinus (i.e., bilobed). Like our native deciduous conifer, the tamarack (Larix laricina), a ginkgo’s fall foliage turns bright yellow before falling off. The species’ common name comes from the leaf’s resemblance to maidenhair fern (Adiantum spp.).

Twigs & Buds. Twigs are stout, smooth and generally grey in colour. There are prominent dwarf shoots along twigs and branches, as well as on twig terminals.

Bark. Ginkgo bark is grey, with flat-topped ridges (younger trees) or fissures (older trees).

Form. Given the species’ long history of cultivation, it may be difficult to discern a natural form for this tree, but some generalizations include relatively sparse branching and maintaining a distinct trunk into the crown. Typical heights are 20-25 metres with 10 metre wide crowns.

Fruit. The fruit is a green drupe, slightly larger than a red cherry, but smaller than a plum. It matures in the autumn and ripens after having been shed. The fleshy exterior of the fruit is rather foul-smelling, with an odour that is frequently described as being reminiscent of rancid butter, and contains a skin irritant. Seed kernels are similar in colour and shape to pistachios, though somewhat larger.

Confusing Species
No other woody species has ginkgo’s unique fan-shaped leaves and prominent dwarf shoots. Butternut, Juglans cinerea, also has bark with grey flat-topped ridges but is easily distinguished by its compound leaves, larger fruit and lack of dwarf shoots.

Habitat
This species prefers moist, sandy, well-drained soils and generous amounts sunlight, but adapts well to a variety of edaphic conditions in most temperate regions of the world. In North America, they are known to thrive in hardiness zones 3 through 8.

Biology
Ginkgos are dioecious and embryo fertilization occurs via free-swimming sperm. In this sense, the species has more in common with other primitive plants like ferns and mosses than with conifers. However, they are still classed as gymnosperms because the ovules are borne naked. They can also reproduce vegetatively via dormant buds at the base of the trunk and, in older specimens, via aerial roots that sprout from the underside of branches and endeavour to contact the soil. Individual specimens can be extremely long-lived, easily exceeding 1,000 years.

Arboriculture
In nurseries, the maidenhair tree is propagated from cuttings and, to a lesser extent, seeds. Male trees are definitely preferred because of the mess and smell created by the fruit, so stem cuttings need to be taken from confirmed male trees. Numerous cultivars have been developed (see table below; also Coder 2003 and Santamour et al 1983).

Ginkgos work well as street and shade trees and are sometimes chosen because of their radiant fall foliage. More importantly, however, ginkgos are an excellent choice for urban environments because they have a high tolerance for air pollution and compacted soils, and also have a remarkably low susceptibility to insects and diseases. Any maintenance activity (i.e., pruning) requires a very light touch and, for otherwise safe mature specimens, deadwood only is a good guideline. Corrective pruning is best done in the form of judicious training cuts on young trees. Of course, ginkgos are as prone as other trees to developing health and safety issues like broken limbs, inward-growing stems, rubbing branches and deadwood. They are said to be good compartmentalizers but that bark wounds do not heal particularly well. For these reasons, they should ideally be planted in more open areas and away from buildings, signage and wires so that eventual size and crown spread will not be an issue that requires corrective pruning.

Beyond their landscape usage, ginkgos are cultivated for leaf production (mostly for use in alternative medicines), seed production (the nut is edible and considered a delicacy in many Asian cultures) and, perhaps not surprisingly given their oriental heritage, as bonsai specimens.

Sidebar 1: Taxonomy
Kingdom: Plantae
Phylum: Ginkgophyta
Class: Ginkgoopsida
Order: Ginkgoales
Family: Ginkgoaceae
Genus: Ginkgo
Species: Ginkgo biloba L.

Common name: maidenhair tree

Latin synonyms: Ginkyo biloba, Pterophyllus salisburiensis, Saliburya biloba, Salisburia adiantifolia

English synonyms: ginkgo, gingko, ginko, kew tree, fossil tree, temple tree, silver apricot

Sidebar 2: Links
Wikipedia: http://en.wikipedia.org/wiki/Ginkgo_biloba

Natureserve: www.natureserve.org/explorer/servlet/NatureServe?searchSciOrCommonName=ginkgo&x=0&y=0

IUCN: www.iucnredlist.org/apps/redlist/details/32353/0

Missouri Botanical Garden: www.mobot.org/gardeninghelp/plantfinder/Plant.asp?code=Z990

USDA Plants Database: http://plants.usda.gov/java/profile?symbol=GIBI2

USDA GRIN: www.arsgrin.gov/cgibin/npgs/html/taxon.pl?17540

CPPIS: www.cbif.gc.ca/pls/pp/ppack.info?p_psn=136&p_type=all&p_sci=sci

The Ginkgo Pages: www.xs4all.nl/~kwanten/index.htm

Sidebar 3: References
Bateman, G. (ed.). “The Oxford Encyclopedia of Trees of the World.” London, England. Peerage Books, 1986: pp.60-61.

Coder, K.D. “Selected Ginkgo Forms and Cultivars.” University of Georgia, Warnell School of Forest Resources Publication FOR0320, 2003.

Coder, K.D. “Tree Sex: Just Say Yes!” Arborist News, Vol.18, No.4, August 2009: p.16.

Farrar, J.L. “Trees In Canada.” Markham, ON: Fitzhenry & Whiteside Ltd., 1995: pp.126-127.

Santamour, F.S. et al. “Checklist of Cultivated Ginkgo.” Journal of Arboriculture, Vol.9, No.3, March, 1983.

Snyder, L.C. “Trees and Shrubs for Northern Gardens.” Minneapolis, MN. University of Minnesota Press, 1980: p.186.

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