Ginkgoales Dr Moni Kumari Date: 28 and 29th September B.Sc 2nd Year PG Botany Department Gaya College, Gaya Ginkgoales is a gymnosperm order containing only one extant species: Ginkgo biloba, the ginkgo tree
It is classified in its
Division: Ginkgophyta
Class: Ginkgoopsida
Order: Ginkgoales
Family: Ginkgoaceae
Genus: Ginkgo
The only extant species within this group
Ginkgo biloba is a highly adaptable plant that can grow in almost any temperate or Mediterranean climate.
Resistant to pollution and pests.
Long lived due to a beneficial combination of disease-resistant characteristics
It can grow up to 30 meters tall and can live for a millenium.
It is also well-known for its unique seeds, which have long been used as a food source in Asia.
Cultivated predominantly in China
Parts of the ginkgo tree are commonly added to foods and drinks or taken as a supplement due to its desirable health benefits. Some old ginkgoes produce aerial roots, known as chichi (Japanese; "nipples") or zhong-ru (Mandarin Chinese), which form on the undersides of large branches and grow downwards. Chichi growth is very slow, and may take hundreds of years to occur
Ginkgoales was, however, very abundantly represented in the world by several species of about 16 genera during the Triassic period of Mesozoic age, i.e. about 200,000,000 years ago.
Today, all the genera, except Ginkgo biloba, are extinct.
Due to the presence of a number of primitive characters, as well as because of its long geological records, Ginkgo is called a “living fossil”.
Details of the geological history of Ginkgoales indicate that its members started appearing on the earth during Permian
Abundance worldwide distribution during Triassic and Jurassic periods of Mesozoic age
Started fading out of existence during Cretaceous
Now represented only in some parts of Southern and Eastern China by only one living member i.e. Ginkgo biloba.
Ramanujam (1976), while tracing the geological history of Ginkgoales, reported that a few records of this order are known from Late Palaeozoic of India. These include Ginkgophyton, Psygmophyllum and Rhipidopsis. Seward (1938) considered Ginkgo “as one of the wonders of the world” and stated that has persisted with little change until the present through a long succession of ages when the earth was inhabited by animals and plants”.
Arnold (1947) mentioned that “Ginkgo biloba is one of the oldest living plants and may indeed be the oldest living genus of the seed plants”
General Characteristics of Ginkgoales:
1. Tall, well-branched trees with short and long shoots. However, some earliest fossil members were without short and long shoots.
2. Wood is pycnoxylic.
It is the compact strong wood with large amount of xylem tracheids or wood and small amount of cortex and pith with little Parenchyma.
3. Leaves are large, leathery and fan-shaped or strap-shaped. They are often deeply divided.
4. Dichotomous venation is usually present in the leaves.
5. Un-branched, catkin-like male organs are axillary in position.
6. Male organs bear micro-sporangiophores.
7. Each micro-sporangiophore possesses 2-12 pendulous microsporangia.
8. Spermatozoids are motile and contain spiral bands of flagella.
9. Ovules are terminal in position on branched or un-branched axillary axes. They are 2-10 in number.
10. Ginkgo biloba has a very distinct appearance characterized by its fan-shaped leaves. 11. Ginkgo is dioecious, which means that pollen-producing structures and ovules are produced on separate trees.
12. The extract of the ginkgo leaves contains flavonoid glycosides and terpenoids (ginkgolides, bilobalides) and has been used pharmaceutically.
13. Mainly used as memory and concentration enhancer, and anti-vertigo agent.