Gymnosperm: Introduction, Characteristics & Classification

Gymnosperms are seed-producing plants that do not produce any covering surrounding the seed i.e. the seed remains naked. The word ‘Gymnosperm’ originates from Gk. ‘gymnos’ meaning ‘naked’ and Gk. ‘sperma’ meaning ‘seeds’.

• A Greek botanist named Theophrastus first used the term ‘Gymnosperm’ in 300 BC in his book

  

  ‘Enquiry into Plants’. He defined gymnosperms as  ‘having or with unprotected seeds’.

• Goebel defined gymnosperms as ‘phanerogams without ovary’.

Good to know

Theophrastus is famously known as the ‘Father of Botany’. He divided plants into four groups:

i. Herb, ii. Shrub, iii. Undershrub and iv. Tree.

Characteristics of Gymnosperms

1. They are perennial and evergreen.
2. Predominantly woody and represented by shrub and trees, not herb.
3. Carpel is not differentiated into ovary, style and stigma.
4. Ovules are borne naked on the surface of megasporophylls.

   

5. Then pollen grains directly fall or settle on micropyles.
6. The endosperm is formed before fertilization. So it is always haploid.
7. Gymnosperms do not reproduce vegetatively by cutting, budding etc.
8. Zygote exhibits free nuclear division.
9. Ovules are not covered by ovary that means ovules only produce seeds, not fruits.
10. Gymnosperms are xerophytic and terrestrial but never aquatic.
11. Plants possess taproots. In some cases, roots show symbiosis with certain algal cells as in coralloid roots or with fungi as in mycorrhizal roots.
12. Coralloid roots are found in Cycas and mycorrhizal roots are found in Pinus.
13. Leaves may be monophorphic (same type of leaf) or dimorphic

    

    (two types: Large green foliage leaf and small brown scale leaf).

14. Flowers are simple and unisexual. No sepal and no petal.
15. Flowers are composed of only microsporophyll and megasporophyll.
16. Gymnosperms are heterosporus and bear different types of spores.
17. Stems are characterized by the presence of collateral endarch.
18. Vessels are absent (exception: Gnetum: the most advanced group in Gymnosperm).
19. Double fertilization doesn’t take place in Gymnosperm.
20. Embryo is developed at the end of a long suspensor.
21. Cleavage polyembryony occurs.
22. Archegonia are produced in the ovules of all Gymnosperms except Gnetum.

Good to know
• The largest gymnosperm in the world is Red Wood tree (Sequoiadendron giganteum) in USA.
• The smallest gymnosperm is Zamia pygmaea.

Placement of Gymnosperm in Plant Kingdom

• Robert Brown first recognized Gymnosperm as a separate group of plants in 1827.
• George Bentham and J.D. Hooker (1883) while classifying Angiosperms placed Gymnosperms between dicotyledons and monocotyledons in their book “Genera Plantarum”.
• Van Tiegham (1898) first recognized Gymnosperms as a major division of Spermatophyta.
  when he divided Spermatophyta into two divisions: The Gymnospermas (Astigmatae) and
  Angiosperms (Stigmatae).

Classification of Gymnosperms

Many systems of classification of gymnosperms have been proposed by different authors.

By Chamberlain (1934)

Coulter and Chamberlain (1917) divided the gymnosperms directly into seven Orders:

1. Cycadofilicales
2. Bennettitales
3. Cycadales
4. Cordaitales
5. Coniferales
6. Ginkgoales
7. Gnetales

Chamberlain (1934) divided Gymnosperms into two classes, viz. Class Cycadophyta and Coniferophyta. They are further subdivided into Orders.

 Class Cycadophyta

The class Cycadophyta includes three orders.

• Order 1. Cycadofilicales : It includes all extinct forms.
• Order 2. Cyacadeoidales: It includes both living and extinct forms.
• Order 3. Cycadales: It includes both living  and extinct forms.

Characteristics of Cycadophyta

• Stems unbranched and stumpy.
• Leaves large and pinnately compound.
• Male cones large and compact with simple sporophylls.
• Female cones loose and consists of pinnate or simple sporophylls.
• Stems have wide cortex.
• Wood is manoxylic.

  

Class Coniferophyta

The class Coniferophyta includes four orders.

• Order 1. Cordaitales: Extinct order.
• Order 2. Coniferales: Includes both extinct and living genera.
• Order 3. Ginkgoales: Includes extinct and one living representative.
• Order 4: Gnetales: Includes both extinct and living genera.

Characteristics of Coniferophyta

• Stems are profusely branched.
• Leaves simple.
• Male and female strobili/ cones are compact and bear bear complex sporophylls.
• Stems have thin cortex.
• Wood is pycnoxylic.

  

By Arnold (1948)

Arnold (1948) divided Gymnosperms into three phyla:

Phylum 1: Cycadophyta

• Order 1: Pteridosparmales,
• Order 2: Cycadeoidales and
• Order 3: Cycadales.

Phylum 2: Coniferophyta

• Order 1: Cordaitales,
• Order 2: Coniferales,
• Order 3: Taxales,
• Order 4: Ginkgoales.

Phylum 3: Chlamydospermophyta

• Order 1: Ephedrales
• Order 2: Gnetales.

By Sporne (1965)

In 1965, Sporne classified Gymnosperms into 3 classes:

Class 1: Cycadopsida

• Order 1: Pteridospermales or Cycadofilicales (Lyginopteris, Glossopteris)
• Order 2: Bennettitales or Cycadeoidales (Cycadeoidea, Williamsonia)
• Order 3: Pentoxylales (Pentoxylon)
• Order 4: Cycadales (Cycas, Abies)

Class 2: Coniferopsida

• Order 1: Cordaitales (Cordaites)
• Order 2: Taxales (Taxus)
• Order 3: Coniferales (Pinus)
• Order 4: Ginkgoales (Ginkgo biloba, living fossil)

Class 3: Gnetopsida

• Order 1: Gnetales (Gnetum, Ephedra, Welwitschia )

Will be added:

1. Difference between- gymnosperm and angiosperm.
2. Difference between- monoxylic and pycnoxylic wood.

Reference

Class Lecture of  Dr. M. Oliur Rahman, Department of Botany, University of Dhaka.

Revised by

1. Tarek Siddiki Taki on 28 July, 2020.
2. Abulais Shomrat on 30 July, 2020. (Needs further revision to add info and images).