General accounts and phylogenetic postion of Ginkgoales

General accounts of Ginkgoales:-
> The order Ginkgoales is today represented by only one living member, i.e. Ginkgo biloba. 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.
> 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:- Some general characteristics of Ginkgoales are under mentioned:
i. Tall, well-branched trees with short and long shoots. However, some earliest fossil members were without short and long shoots.
ii. Wood is pycnoxylic.
iii. Leaves are large, leathery and fan-shaped or strap-shaped. They are often deeply divided.
iv. Dichotomous venation is usually present in the leaves.
v. Un-branched, catkin-like male organs are axillary in position.
vi. Male organs bear micro-sporangiophores.
vii. Each micro-sporangiophore possesses 2-12 pendulous microsporangia.
viii. Spermatozoids are motile and contain spiral bands of flagella.
ix. Ovules are terminal in position on branched or un-branched axillary axes. They are 2-10 in number.
x. Seeds are large-sized.
xi. Each seed contains a fleshy outer layer and a middle stony layer.

Phylogenetic postion of Ginkgoales:- Some of the striking peculianties of Ginkgo biloba, the only living representative of Ginkgoales, include:
i. Bilobed, fan-shaped leaves with dichotomous open venation,
ii. Ovule bearing a collar at the base,
iii. Micro-sporangiophore bearing a hump-like outgrowth at its apex,
iv. Presence of tent pole at the tip of the female gametophyte, and
v. Absence of suspensor in its embryo.
Resemblances with Cordaitales:-
i. Presence of double leaf trace.
ii. Endospermic beak in the mature ovule.
iii. The probable motility of the spermatozoids of the members of both Ginkgoales and Cordaitales are some of the resemblances between these two groups.
Resemblances with Pteridospermales:-
i. Presence of leaf gap in the stem.
ii. Dichotomous open venation in the wedge-shaped leaves of Ginkgo and pinnules of some seed ferns (Ptendospermales).
iii. A distinct pollen chamber.
iv. A massive fleshy layer in the ovules.
v. Collar at the base of the ovules in Ginkgo and cupule in ovules of some Pteridospermales.
Resemblances with Filicales:-
i. The similarities between the primary xylem structure, secondary xylem structure and periderm of Ginkgo and some ferns (Ophioglossum and Botrychium).
ii. Dichotomous open venation in their leaves.
iii. Multi-flagellated and motile spermatozoids.
iv. Presence of ventral canal cell in the archegonia in some of their members.
Resemblances with Cycadales:-
i. Presence of multi-flagellated spermatozoids.
ii. Well-developed nucellar beak and pollen chamber.
iii. Haustorial nature of pollen tube.
iv. Presence of large egg, massive female gametophyte and well-developed venter.
v. Endoscopic embryo with two cotyledons.
vi. Seed with thick and well-developed integument.
vii. Hypogeal type of seed germination.
Resemblances with Coniferales:-
i. General appearance of tree is cone like.
ii. Extensively branched stem with two types of branches, i.e. long shoots and dwarf shoots.
iii. Leaves are simple with sunken stomata.
iv. Cortex and pith are narrow and wood is pycnoxylic.
v. Secondary wood is well-developed.
vi. Medullary rays are uniseriate.
vii Circular bordered pits arranged uniseriately along the radial walls of the tracheids.
viii. Microsporangia show longitudinal dehiscence.
ix. Sessile nature of ovule.

Ginkgo biloba:-
Classification:-
Division - Coniferophyta
Class - Coniferopsida
Order - Ginkgoales
Family - Ginkgoaceae
Genus - Ginkgo 
Species - biloba
Distribution of Ginkgo:-
> Ginkgo biloba is a tall, slender and beautiful tree. 
> It is commonly called Maiden-hair Tree because its new leaves resemble very much like those of Adiantum (called maiden hair fern) both in form and venation.
>  It is the oldest living seed plant. 
> It is cultivated for its edible seeds in some parts of China and Japan. 
> Ginkgo still exists in the wild state in South-eastern China, along “the north western border of Chekiang and south eastern Anhwei”. 
> In China and Japan it is grown as a sacred tree in temple gardens. 
> It is cultivated in the United States as a shade tree. 
> t is also successfully cultivated in some gardens of Europe, America and India.
Ginkgo: A Living Fossil:-
> Ginkgo is known to have occurred in rocks as old as Triassic or even much earlier. 
> Fossils of its leaves have been identified in the Permian and probably also in the Carboniferous. Ginkgo biloba occurs even today. It is, therefore, referred as living fossil by the botanists. Or, it may also be referred as the oldest living seed plant.
> The plant body of Ginkgo biloba is sporophytic, and the sporophyte resembles several conifers in
general habit. 
Description of Tree:-
Stem:-
> Ginkgo usually matures to about 80' tall by 60 wide.
> Trunk may get up to 3' in diameter with age.
> Alternate Branching.
> Ginkgo can live up to 100,000 years. Ginkgo Biloba is one of the oldest living tree species, dating back over 300 million years.
Leaves:-
> Ginkgo is deciduous.
> Alternate arrangement.
> Simple blade
> Simple from
> 2 lobed apex,
> Acute base,
> Fan-shaped,
> Leaves fall color is usually a green yellow. However, can be a golden-yellow when growing under excellent conditions.
Roots:-
> Roots bear deep into ground to provide stable base and support for tree. 
> Roots branch over wide area.
Reproduction:-
> Ginkgo is dioecious, meaning male and female flowers are borne on separate trees.
> Hanging catkins on male trees pollinate the hanging pistillate flowers on 2" peduncles onfemale trees in March and April.
> Ginkgo may not flower or fruit until it is about twenty years old.
> Wind is the main transporter of pollen for the ginkgo tree.Fruits on female trees are an abundant tan-orange oval fruit which hang from the spur shoots.
> Fruits have very foul smell.-Since male trees produce no fruit, they are most commonly planted.
Ginkgo Economic Importance:-
> Ginkgo biloba tree is treated as a sacred plant in China and Japan and worshipped by the people.
> It is regarded as “Holy Tree” by Buddhist monks and nuns because of its tall, strong and majestic
appearance. 
> It is grown as an ornamental plant in gardens in several countries.
> In autumn, the green leaves turn yellow, showing a magnificent autumn scenery. 
> The endosperm of its roasted seeds is edible, but seeds may prove fatal if taken in large quantity. 
> After the outer skin of its apricot-like seeds is peeled off or decayed, the kernel left is called ” White
Fruit”. Ginkgo is, therefore, also named “White fruit tree”.
> The kernel is also used as food and Chinese medicine as well. If it is taken raw, it functions as
detoxicating and asthma-curing medicine. 
> Although the plants are highly resistant to pathogenic infections, specially of bacteria and fungi, their wood is not of much commercial importance. 
> It also possesses a strong capacity of resistance to air pollution by smoke and poisonous gases.
> Since an unpleasant odour is emitted from the ripe seeds of female trees, male trees are largely
preferred and grown as shade trees in China, Japan and United States. 
> Ginkgo trees grow and develop very slowly. It is said that the tree planted by grandfather will bear “fruit” at the time when his grandson grows up. Therefore, it is also known as “grandfather grandson tree”.
> An extract of leaves of G. biloba is useful in the treatment of cerebral insufficiency and vertigo.