Classification and Distribution of Gymnosperm in India

  Classification and Distribution of Gymnosperm in India 

Phanerogams are the collective term for gymnosperms and angiosperms (phanero = exposed, gams = sex organs or spermatophytes; sperma = seed).

• Plants with bare seeds are known as gymnosperms. The ovules in gymnosperms are openly visible both before and after fertilization. They are not contained by the ovarian wall. of contrast, the ovule or ovules of angiosperms are entirely encased within a structure known as the ovary. For this reason, only naked seeds are produced in gymnosperms instead of fruits, but in angiosperms, seeds are produced inside fruits.

• Coulter and Chamberlain (1910) divided gymnosperms into 7 orders. Some of the orders are extinct today. 

The seven orders are as follows: 

1. Cycadofilicales (extinct) 

2. Bennettitales (extinct) 

3. Cycadales (Mesozoic to present day) 

4. Cordaitales (extinct) 

5. Ginkgoales (Palaeozoic to present day) 

6. Coniferales (Palaeozoic to present day) 

7. Gnetales (recent)

Chamberlain (1934) divided Gymnosperms into two large groups: 

A. Cycadophyta – sporophylls are in cones. They include three orders: 

1.Cycadofilicales (Pteridospermae) 

2.Bennittitales (Cycadeoideales) 

3.Cycadales 

B. Coniferophyta- are divided into four orders: 

1. Ginkgoales 

2. Cordaitales 

3. Coniferales

 4. Gnetales 

The following are some crucial traits of gymnosperms:

• They don't make flowers.
• No seeds develop inside of a fruit. They're bare-chested.
• They can be found in cooler climates with snowfall.
• They grow leaves that resemble needles.
• They grow into shrubs or trees and are woody or perennial.
• They are not separated according to stigma, style, or ovary.
• They are pollinated directly by the breeze since they lack stigma.
• Only one of the two gametes produced by the male gametophytes is viable.
• They develop reproductive organs into cones.
• The endosperm found in seeds contains nutrients necessary for the plant's growth and development.
• Vascular tissues of these plants aid in the movement of water and nutrients.
• There are no vessels in the xylem, no partner cells in the phloem, and sieve tubes 

The cyanophyta
Because cycads are dioecious, individual plants can only be male or female. The bulk of cycads, which are plants that carry seeds, are now extinct. They had been at their height in the late Triassic and Jurassic periods. These days, the plants are regarded as historical artifacts.
Large compound leaves, robust trunks, and tiny leaflets joined to a single central stem are typical features of these plants. Their heights vary widely, from a few centimeters to several meters.
Typically, cycads can be found in tropical and subtropical regions. Certain individuals have adapted to dry, arid climates, while others have done so to swampy, oxygen-poor surroundings.

Ginkgophyta
There is only one extant species in the Ginkgophyta class of Gymnosperms. The remaining members of this class have all vanished.

The enormous size and fan-like leaves of ginkgo trees define them. Ginkgo trees can be used for a wide range of purposes, including cooking and healing. Ginkgo leaves are consumed to treat memory-related conditions such as Alzheimer's.

In addition to its resistance to disease and insect infestation, ginkgo trees also exhibit high levels of pollution resistance. They are so hardy that, within a kilometer or two of the blast radius, just six Ginkgo trees survived the detonation of the nuclear bombs on Hiroshima.

Gnetophyta
Like all other members of the gymnosperm family, gnetophytes are also extinct species. There are currently just three members of this genus.

Typically, gnetophytes are made up of trees, shrubs, and tropical plants. Their softly coated, floral leaves are defining characteristics. This covering demonstrates a common ancestor with angiosperms.

Because they have vessel elements in their xylem, genotrophytes are distinct from other members of this class.

Coniferophyta
Within the gymnosperm family, these are the species that are most widely known. Since they never lose their leaves in the winter, they are considered evergreen. Their primary distinguishing feature is the formation of needle-like structures by male and female cones.

Temperate zones, with an average temperature of 10 °C, are home to coniferous trees. Conifers include giant sequoia, pines, cedar, and redwood.

Jefferey (1917) recognizes two classes among gymnosperms s follows

A. Class Arachigymnospermae- It includes all those gymnosperms that resemble from their general appearance and anatomy. They possess motile spermatozoids. He divided this class into five orders

1 Order Pteridospermae- it includes all extinct forms, primitive and that lived in Paleozoic period. 

2. Order Cycadeodea- It includes all extinct forms. 

3. Cycadales- Includes extinct and living forms.

 4. Order Cordaitales- Includes all extinct forms. 

5. Order Ginkgoales- Includes extinct and single living genera. 

B. Metagymnospermae -

i) plants of this class possess simple leaves and have no resemblance to the ferns. 

ii) Possess non- motile male gametes, the pollen gains grow into a pollen tube. It includes two orders

1 Order Coniferales- It includes living genera e.g. Pinus, Cedrus, Taxus, Podocarpus, Taxodium etc. also includes fossil genera. 

2 Order Gnetales- Includes Ephedra, Gnetum and Welwitschia and many fossil genera. 

On the basis of composition of wood the gymnosperms were divided into two classes

i) Metaxylic- when possess porous wood and loose texture. 

ii) Pycnoxylic- When the wood was compact 

The former includes Cycadales, Cycadeiodales and Cycadofilicales while the latter includes Cordaitales, Ginkgoales, Coniferales and Gnetales. This classification was given by Soward (1919). However, Chamberlain in 1934 divided the gymnosperms into two classes which were further divided into orders with their respective characters such as-

A. Class Cycadophyta- 

i) Most of the plants of this group are unbranched, stems are stumpy. 

ii) Male cones large and compact with simple sporophylls bear large ovule.

 iii) Anatomically the stems have wide cortex and monoxylic wood. 

This class includes three ordersa) 

Cycadofilicales- Includes extinct forms and fossils. 

b) Cycadeiodales-Includes both living and fossil forms. 

c) Cycadales- Includes both living and fossil forms. 

B. Class- Coniferophyta- 

i) profusely branched stem is the characteristic feature of this group.

 ii) Leaves simple and the foliage given leaf like appearance. 

iii) Both the strobili- male and female are compact and bear complex sporophylls. 

iv) Wood is pycnoxylic. 

It includes four ordersa. Cordaitales- It Includes extinct order. 

b. Ginkgoales- It includes extinct and only one living representative- Ginkgo biloba. 

c. Coniferales- It includes both extinct and living forms. 

d. Gnetales- Includes both living and extinct forms.

D. D. Pant (1957) has proposed a classification of Gymnosperms in which the group is divided into three divisions 

a) Cycadophyta 

ii) Clamydospermatophyta and 

iii) Coniferophyta 

An outline of Pant’s (1957) scheme of classification of gymnosperms is as follows:

After that Andrew (1961) another renowned scientist classified Gymnosperms and divided it into six divisions as

i) Pteridospermatophyta 

ii) Cycadophyta. 

iii) Ginkgophyta

 iv) Coniferophyta. 

v) Gnetophyta and 

vi)Gymnosperms of uncertain affinities. 

K. R. Sporne in 1965 classified Gymnosperms in his book namely “The Morphology of Gymnosperms” based on Pilger and Melchior (1954) classificationGymnosperms- divided into three divisions 

1. Cycadopsida 2. Coniferopsida and 3. Gnetopsida 

These divisions further divided into orders

1. Division Cycadopsida

Order 

1. Pteridospermales- 

Families-(7)-

1. Lyginopteridaceae- (Lyginopteris) 

2- Medulosaceae (Medulosa) 

3- Calamopteridaceae (Calamopitys) 

4- Glossopteridaceae (Glossopteris) 

5- Peltospermaceae (Xylopteris) 

6- Corystospermaceae (Xylopteris) 

7-Caytoniaceae (Caytonia) . 

Order 2. Bennettitales - Families (3) 

1- Williamsoniaceae (Williamsonia) 

2. Wielandiellaceae (Wielandiella) 

3. Cycadeoideaceae (Cycadeidea)

Order 3. Pentoxylaes -Family(1) 

1. Pentoxylaceae (Pentoxylon), Sahnia)

Order 4. Cycadales-Family(2) 

1. Cycadaceae (Cycas, Zamia etc.)

 2. Nilssoniaceae (Nilssonia)

 2. Division Coniferopsida

 Order 

1. Cordaitales –Families (3)

 1. Ertophytaceae (Eristophyton) 

2. Cordaitaceae (Cordaites)

 3. Poroxylaceae (Poroxylon)

Order 2. Coniferales –Families (9) 

1. Lebachiaceae (Lebachia) 

2. Votziaceae (Voltziopsis) 

3. Palissyaceae (Palissya) 

4. Pinaceae (Pinus, Abies, Picea) 

5. Taxodiaceae (Taxodium) 

6. Cupressaceae (Cupressus) 

7. Podocarpaceae (Podocarpus) 

8. Cephalotaxaceae (Cephalotaxus)

9. Araucariaceae (Araucaria, Agathis)

 

Order 3. Taxales- Family 

(1) Taxaceae (Taxus, Torreya) 

Order 4. Ginkgoales.-Families (2) 

1. Trichoptyaceae (Trichopitys) 

2. Ginkgoaceae (Ginkgo) 

3.Division Gnetopsida Order 1. Gnetales.- Families (3) 

1. Gnetaceae (Gnetum) 

2. Welwitschiaceae (Welwitschia) 

3. Ephedraceae (Ephedra)

Recently (1980) Taylor classified Gymnosperms in six divisions as 

1. Progymnospermophyta, 2. Pteridospermophyta. 3. Cycadophyta. 4. Cycadophyta. 5. Ginkgophyta. 6. Coniferophyta. 

Thus after reviewing the different theories and outlines of classification of Gymnosperms adopted by different works from time to time it shows that there are great controversies regarding the classification of Gymnosperms. But even then the last and the most important classification may be taken as correct one for studies. 

Stewart (1983) placed Progymnosperpsida, Gymnospermopsida and Gnetopsida as distinct classes under the division Tracheophyta, the vascular plants of kingdom Plantae. These three classes were further divided as-

Kingdom Plantae

Division Tracheophyta 

Class - 1. Progymnospermopsida 

Order - A. Aneunophytales B. Aracheopteridales C. Protopityles

 Class 2. Gymnospermopsida

 Order - A. Pteridospermales G. Gimkgoales B. Cycadales H. Cordaitales C. Cytoniales I. Voltziales D. Glossopteridales K. Coniferales E. Pentoxylales L. Taxales

Class 3. Gnetopsida 

Order A. Gnetales B. Ephedrales C. Welwitschiales. 

Birbal Sahni (1920 a), based on morphological nature of ovule bearing organ and axial or foliar nature of ovules divided gymnosperms into two major groups- Stachyspermae ) ovules arise on the axial organ or stem) spread over orders- Cordaitales, Ginkgoales, Coniferales, Taxales and Cycadales and Cycadofilicales as Phyllospermae (ovules borne on leaves).

Gymnospermae

1. Phyllospermae 2. Stachyspermae 

A. Cycadofilicales A. Cordaitales B. Bennettitales 

B. Ginkgoales 

C. Cycadales and C. Coniferales. D. Taxales.

Christenhusz et al., (2011) proposed a new classification and linear sequence of the extant gymnosperms based on molecular and morphological phylogenetic studies. 

They divided all extant gymnosperms into 4 sub classes, 8 orders and 12 families as follows

Sub Class I. Cycadidae 

Order A. Cycadales 

Family 1. Cycadaceae 

Family 2. Zamiaceae 

Sub Class II Ginkgoidae 

Order B. Ginkgoales 

Family 3. Ginkgoaceae 

Sub Class III Gnetidae 

Order C. Welwitschiales

 Family 4. Welwitschiaceae Order D. Gnetales Family 5. Gnetaceae Order E. Ephedrales Family 6. Ephedraceae Sub class IV Pinidae Order F. Pinales Family 7. Pinaceae

Order G. Araucariales Family8. Araucariaceae Family9. Podocarpaceae Order H. Cupressales Family10. Sciadopityaceae Family11.Cupreassaceae Family12. Taxaceae. 

Distribution of Gymnosperm in India 

Some gymnosperm groups are completely extinct, while others can still be found in living forms and as prehistoric fossils. However, there are still certain groups that are mostly found in live gymnosperms that are found in arctic, tropical, and temperate regions. Gymnosperms are mostly evergreen xerophytes.
There are about seventy genera and seventy-five species of gymnosperms in the world today. India has been reported to have 16 genera and 53 species (M. B. Raizada and K. C. Sahni, 1960).
Only 14 genera were listed by Maheshwari. The primary reason for the lower number of representatives is their environment; gymnosperms are primarily found in temperate regions of India, and only the Himalayas provide such a climate.

The majority of gymnosperms are found in the eastern and western Himalayas, as well as in certain other parts of India, because they create vast forests and flourish profusely in the several Himalayan mountains.

Gymnosperms are classified into six extant orders, four of which are found in India. Cycadales, Coniferales, Ephedrales, and Gnetales are a few of these. In India, there are four species of cicadas that represent the clade.

The Indian flora has a very low representation of gymnosperms. A few species of Cycas, Podocarpus, and Gnetum are representative of them over the wide peninsula of India. But only conifers make up the gymnosperms found in the extra-Peninsular Himalayas and, to a lesser extent, in the associated mountains of Kashmir, Assam, and Arunachal Pradesh, which encompass a sizable area of forested territory.

Among the gymnosperms, the Coniferales are the most common and highly populated group. Other groupings in this category include Cycads, Ginkgoales, Gnetales, and Conifers. As of right now, Pinus, Cedrus, Abies, Larix, Picea, Cupressus, Tsuga, Juniperous, Taxus, Araucaria, Thuja, Podocarpus, and Cephalotaxus are common species that represent this group.

The Himalayas are home to most conifers, with the north-west Himalayas (Uttarakhand, Kashmir, Himachal Pradesh, etc.) having the highest concentration of these forests.

Their distribution usually lies between 1800 and 3300 meters above sea level and is determined by height. While other Pinus species have been documented from the Khasya region of Assam and the hillocks of East Bengal, respectively (Pinus insularis, 700–1,850 m asl., and Pinus merkusii, 150–600 m asl. in Assam).

Only the genus Cycas, which includes the species C. circinalis, C. beddomei, C. pectinata, and C. rumphii, is found in India. In addition, the Japanese native C. revolute is frequently grown in Indian gardens.

Some foreign species, including those of Zamia, Macrozamia, Encephalortos, and Stangeria, are grown in Indian gardens on occasion. In a similar vein, a few native Chinese trees known as Ginkgo biloba can be found grown in Indian gardens.

In India, there are several species of Ephedra and Gentum belonging to the Gnetales order. Six of the seven species of Ephedra are restricted to the northwest Himalayan regions, and only one, E. foliate, is found on the plains of Rajasthan and Punjab.